A portable spinal orthotic backrest, comprising a back support plate, the back support plate being integrally formed of a plastic material and comprising, from top to bottom in a vertical direction: an upper portion having a vertical, central longitudinal cross-section with an inner-side curvature conforming to a kyphotic curvature of a person's thoracic vertebrae, the upper portion having an inner side protrudingly provided with a plurality of protruding knobs corresponding in positions along two lateral sides of the thoracic vertebrae, the upper portion having a horizontal transverse cross-section with an inner-side curvature conforming to a horizontal curvature of the person's back that corresponds in position to the thoracic vertebrae, the inner side of the upper portion being concave and having an upwardly decreasing width; and a lower portion having a vertical, central longitudinal cross-section with an inner-side curvature conforming to a lordotic curvature of the person's lumbar vertebrae, the lower portion having an inner side protrudingly provided with a plurality of protruding knobs corresponding in positions along two lateral sides of the lumbar vertebrae, the lower portion having a horizontal transverse cross-section with an inner-side curvature conforming to a horizontal curvature of the person's back that corresponds in position to the lumbar vertebrae, the inner side of the lower portion being concave and having a downwardly decreasing width such that a joining section between the upper portion and the lower portion extends to two lateral sides of the person's back that are adjacent to a joining section between a bottom end of the thoracic vertebrae and an upper end of the lumbar vertebrae; and at least two suspension braces, wherein each said suspension brace is made of a metal or a rigid plasticized material, is installed on a backside of the back support plate along the vertical direction, and has two ends respectively fixed to the upper portion and the lower portion such that each said suspension brace extends across the joining section between the upper portion and the lower portion. an upper portion having a vertical, central longitudinal cross-section with an inner-side curvature conforming to a kyphotic curvature of a person's thoracic vertebrae, the upper portion having an inner side protrudingly provided with a plurality of protruding knobs corresponding in positions along two lateral sides of the thoracic vertebrae, the upper portion having a horizontal transverse cross-section with an inner-side curvature conforming to a horizontal curvature of the person's back that corresponds in position to the thoracic vertebrae, the inner side of the upper portion being concave and having an upwardly decreasing width; and a lower portion having a vertical, central longitudinal cross-section with an inner-side curvature conforming to a lordotic curvature of the person's lumbar vertebrae, the lower portion having an inner side protrudingly provided with a plurality of protruding knobs corresponding in positions along two lateral sides of the lumbar vertebrae, the lower portion having a horizontal transverse cross-section with an inner-side curvature conforming to a horizontal curvature of the person's back that corresponds in position to the lumbar vertebrae, the inner side of the lower portion being concave and having a downwardly decreasing width such that a joining section between the upper portion and the lower portion extends to two lateral sides of the person's back that are adjacent to a joining section between a bottom end of the thoracic vertebrae and an upper end of the lumbar vertebrae; and at least two suspension braces, wherein each said suspension brace is made of a metal or a rigid plasticized material, is installed on a backside of the back support plate along the vertical direction, and has two ends respectively fixed to the upper portion and the lower portion such that each said suspension brace extends across the joining section between the upper portion and the lower portion.