The invention belongs to the field of motion control of numerical control systems and specifically relates to a rounding error compensation method for S-curve acceleration and deceleration. After primary S curve planning, an acceleration segment, a constant-speed segment and a deceleration segment cannot exist at the same time. Different error compensation strategies need to be adopted aiming at different combination types according to analysis on above motion parameter relation. When the constant-speed segment is in presence, a displacement adjustment method is selected. When the constant-speed segment is in absence while the acceleration segment and the deceleration segment are in presence at the same time, a maximal speed adjustment method is selected. When the constant-speed segment isin presence and the displacement of the constant-speed segment is comparatively short and cannot meet adjustment requirements, displacement adjustment is employed first and then speed adjustment is employed. According to the invention, single-segment interpolation time is not adjusted and the interpolation total time is adjusted only. Interpolation time of compensation is reduced as far as possible, so that the interpolation efficiency is improved. Based on the adjusted interpolation time, all motion parameters are calculated again by using the displacement and speed adjustment methods, so that a condition that the motion parameters do not surpass limits after adjustment is ensured.