A method for designing a multi-link engine comprising: an engine block body including at least one cylinder; a piston reciprocally disposed inside the cylinder of the engine block body; an upper link having a first end pivotally connected to the piston by a piston pin; a lower link rotatably mounted on a crankpin of a crankshaft and connected to a second end of the upper link by an upper pin; and a control link having a first end and a second end, the first end of the control link being rotatably connected to the lower link by a control pin and the second end of the control link being pivotally mounted on a pivot portion of a control shaft, characterized in that: the lower link has a coupling hole with the crankpin disposed in the coupling hole such that a center of gravity (G I) of the lower link and a center axis of the crankpin are both located on a line passing through a center axis of the upper pin and a center axis of the control pin and positioned between the center axes of the upper pin and the control pin, the crankshaft has a flywheel provided on a shaft end portion thereof, and the upper link, the lower link and the control link are configured and arranged with respect to each other to satisfy: m l x gl 0 L 2 + m c x gc 0 L 3 − m u x gu 0 L 6 L 4 L 2 = 0 where m l is a mass of the lower link, x gl0 is a distance from the center axis of the crankpin to the center of gravity (G I) of the lower link, L 2 is a length from the center axis of the crankpin to the center axis of the control pin, m c is a mass of the control link, x gco is a distance from a center axis of the pivot portion of the control shaft to a center of gravity (G c) of the control link, L 3 is a length from the center axis of the control pin to the center axis of the pivot portion of the control shaft, m u is a mass of the upper link, x guo is a distance from a center axis of the piston pin to a center of gravity (G u) of the upper link, L 4 is a length from the center axis of the upper pin to the center axis of the crankpin, and L 6 is a length from the center axis of the piston pin to the center axis of the upper pin. an engine block body including at least one cylinder; a piston reciprocally disposed inside the cylinder of the engine block body; an upper link having a first end pivotally connected to the piston by a piston pin; a lower link rotatably mounted on a crankpin of a crankshaft and connected to a second end of the upper link by an upper pin; and a control link having a first end and a second end, the first end of the control link being rotatably connected to the lower link by a control pin and the second end of the control link being pivotally mounted on a pivot portion of a control shaft, characterized in that: the lower link has a coupling hole with the crankpin disposed in the coupling hole such that a center of gravity (G I) of the lower link and a center axis of the crankpin are both located on a line passing through a center axis of the upper pin and a center axis of the control pin and positioned between the center axes of the upper pin and the control pin, the crankshaft has a flywheel provided on a shaft end portion thereof, and the upper link, the lower link and the control link are configured and arranged with respect to each other to satisfy: m l x gl 0 L 2 + m c x gc 0 L 3 − m u x gu 0 L 6 L 4 L 2 = 0 where m l is a mass of the lower link, x gl0 is a distance from the center axis of the crankpin to the center of gravity (G I) of the lower link, L 2 is a length from the center axis of the crankpin to the center axis of the control pin, m c is a mass of the control link, x gco is a distance from a center axis of the pivot portion of the control shaft to a center of gravity (G c) of the control link, L 3 is a length from the center axis of the control pin to the center axis of the pivot portion of the control shaft, m u is a mass of the upper link, x guo is a distance from a center axis of the piston pin to a center of gravity (G u) of the upper link, L 4 is a length from the center axis of the upper pin to the center axis of the crankpin, and L 6 is a length from the center axis of the piston pin to the center axis of the upper pin. the lower link has a coupling hole with the crankpin disposed in the coupling hole such that a center of gravity (G I) of the lower link and a center axis of the crankpin are both located on a line passing through a center axis of the upper pin and a center axis of the control pin and positioned between the center axes of the upper pin and the control pin, the crankshaft has a flywheel provided on a shaft end portion thereof, and the upper link, the lower link and the control link are configured and arranged with respect to each other to satisfy: m l x gl 0 L 2 + m c x gc 0 L 3 − m u x gu 0 L 6 L 4 L 2 = 0 where m l is a mass of the lower link, x gl0 is a distance from the center axis of the crankpin to the center of gravity (G I) of the lower link, L 2 is a length from the center axis of the crankpin to the center axis of the control pin, m c is a mass of the control link, x gco is a distance from a center axis of the pivot portion of the control shaft to a center of gravity (G c) of the control link, L 3 is a length from the center axis of the control pin to the center axis of the pivot portion of the control shaft, m u is a mass of the upper link, x guo is a distance from a center axis of the piston pin to a center of gravity (G u) of the upper link, L 4 is a length from the center axis of the upper pin to the center axis of the crankpin, and L 6 is a length from the center axis of the piston pin to the center axis of the upper pin.