The present invention provides a portable spinal orthotic backrest, which comprises a back supporting sheet integrally formed with plastic material including an upper portion and a lower portion from top to bottom along a vertical direction, wherein the upper portion has an inner curvature of the center longitudinal cross-section along the vertical direction to be matched with the curvature of human body thoracic vertebra as a curve while the thoracic spine protrudes backward. The positions on the inner side of the upper portion corresponding to both sides of thoracic vertebra are respectively protruded with a plurality of protrusions. The inner curvature of the upper portion for the cross-section along the horizontal direction is matched with the curvature of human back corresponding to the thoracic vertebra along the horizontal direction. The inner side of the upper portion is concaved inwardly, and has its width as a structure having narrow upper portion and wide lower portion. The lower portion has an inner curvature of the center longitudinal cross-section along the vertical direction to be matched with the curvature of human body lumbar vertebra as a curve while the lumbar spine protrudes forward. The positions on the inner side of the lower portion corresponding to both sides of lumbar vertebra are respectively protruded with a plurality of protrusions. The inner curvature of the lower portion for the cross-section along the horizontal direction is matched with the curvature of human back corresponding to the lumbar vertebra along the horizontal direction. The inner side of the lower portion is concaved inwardly, and has its width as a structure having wide upper portion and narrow lower portion, such that the joint of the upper and lower portions may be extended to left and right sides of human back near the joining portion between bottom end of thoracic vertebra and top end of lumbar vertebra. Thus, because the backrest has a simple structure and does not o
