Matrix of deviation for spatial modulating spectropolarimeter that composed of quarter wave plate, double birefringent wedges and polarizer is educed. Magnitude of influence of element deviation to emergent light is figured out, with that the modulative phase retardance is equal to 0 or 0.5π. It is presented that, when retardant phase is 0.5π and its deviation is 0.02π, the modulating coefficient of Stokes parameter V is 0.0314. And when V=0.2, it will cause that the probability of restraint for measuring deviation of Stokes parameter U under 0.45%, is decreased from about 80% to 6%, compare with V=0. By simulation analysis, it is presented that the relative measuring deviation of degree of linear polarization (DOLP) is less than 0.5% without instrument polarization calibrating, when all the element deviations are equal to the positive maximum in their span of deviation, and the Stokes parameter V≤0.04.