A motion-mode- and thumb-position-based motion control system of a myoelectric hand, the motion-mode- and thumb-position-based motion control system comprising: a motion mode switching unit configured to switch a motion that is performed by the myoelectric hand between a hand motion mode for intention and emotion expression and a grasping motion mode for holding an object to change a controller to be enabled; characterized in that it further comprises a thumb sensor configured to determine whether a thumb provided at the myoelectric hand is located at a horizontal position or a vertical position to implement a vertical thumb motion mode and a horizontal thumb motion mode; a hand motion controller configured to, when a main hand motion detailed motion mode or a subsidiary hand motion detailed motion mode matched with each of the horizontal thumb motion mode and the vertical thumb motion mode depending on a position of the thumb is selected in the hand motion mode enabled by the motion mode switching unit, receive an electromyography signal transmitted from at least one of first and second electromyography sensors attached to a human body, to enable a control signal for driving the myoelectric hand in order to implement a hand motion matched with the main hand motion detailed motion mode or the subsidiary hand motion detailed motion mode, and to transmit the control signal to a driving unit of the myoelectric hand; and a grasping motion controller configured to, when a main grasping motion detailed motion mode or a subsidiary grasping motion detailed motion mode matched with each of the horizontal thumb motion mode and the vertical thumb motion mode depending on the position of the thumb is selected in the grasping motion mode enabled by the motion mode switching unit, receive an electromyography signal transmitted from at least one of the first and second electromyography sensors, to enable a control signal for driving the myoelectric hand in order to implement a grasping motion matched with the main grasping motion detailed motion mode or the subsidiary grasping motion detailed motion mode, and to transmit the control signal to the driving unit of the myoelectric hand, wherein the motion mode switching unit switches between the hand motion mode and the grasping motion mode through a plurality of combined signals applied from the first and second electromyography sensors to change the controller to be enabled. a motion mode switching unit configured to switch a motion that is performed by the myoelectric hand between a hand motion mode for intention and emotion expression and a grasping motion mode for holding an object to change a controller to be enabled; characterized in that it further comprises a thumb sensor configured to determine whether a thumb provided at the myoelectric hand is located at a horizontal position or a vertical position to implement a vertical thumb motion mode and a horizontal thumb motion mode; a hand motion controller configured to, when a main hand motion detailed motion mode or a subsidiary hand motion detailed motion mode matched with each of the horizontal thumb motion mode and the vertical thumb motion mode depending on a position of the thumb is selected in the hand motion mode enabled by the motion mode switching unit, receive an electromyography signal transmitted from at least one of first and second electromyography sensors attached to a human body, to enable a control signal for driving the myoelectric hand in order to implement a hand motion matched with the main hand motion detailed motion mode or the subsidiary hand motion detailed motion mode, and to transmit the control signal to a driving unit of the myoelectric hand; and a grasping motion controller configured to, when a main grasping motion detailed motion mode or a subsidiary grasping motion detailed motion mode matched with each of the horizontal thumb motion mode and the vertical thumb motion mode depending on the position of the thumb is selected in the grasping motion mode enabled by the motion mode switching unit, receive an electromyography signal transmitted from at least one of the first and second electromyography sensors, to enable a control signal for driving the myoelectric hand in order to implement a grasping motion matched with the main grasping motion detailed motion mode or the subsidiary grasping motion detailed motion mode, and to transmit the control signal to the driving unit of the myoelectric hand, wherein the motion mode switching unit switches between the hand motion mode and the grasping motion mode through a plurality of combined signals applied from the first and second electromyography sensors to change the controller to be enabled.