in most of the researches of polarization aberration, the influence of diattenuation is not large enough to affect imaging quality evidently. however, the modulation transfer function decreases when optical elements with complex planar dielectric structures and low transmittance, such as beam-splitter and optical modulator, are introduced into an imaging system. in this paper, a vector optical model in descartes coordinate system is proposed based on the concept of vector plane wave spectrum (vpws). the results of calculation show that the vpws model is consistent with debye model. compared with debye vector diffraction integral, the vpws method is more suitable to the description of the pa introduced by planar optical device with opaque mask, such as larger surface quantum-confined-stark-effect electroabsorption modulator, which is used to modulate the light collected by optical antenna of time-of-flight (tof) depth system or modulating-retroreflector free-space-optical communication system. in order to simplify the calculation and obtain the conclusion of the change in imaging quality directly, the formula of optical transfer function is decomposed into three parts (te component, tm component and the correlation of them) instead of polynomial expansion of pupil function. the influences of diattenuation on mtf is studied globally and locally in a range of cut-off frequency of optical imaging system (2 n a/lambda). allowance of diattenuation is analysed by numerical calculation, and a mathematical expression is derived. the result shows that the change of diattenuation can be neglected when the spatial frequency v is less than 0.2 n a /lambda, and the range of allowance decreases with the increase of spatial frequency. according to numerical calculation shown in fig. 7 and the derived formulas (15) and (16), the ratios of reflection/transmission coefficient of s-light and p-light p root d-alpha ff should range respectively from 0.63 to 1.6(0.2 n a /lambda < v < 0.8 n a /lambda) and from 0.9 to 1.11(v > 0 : 8 n a /lambda) when the mtf is required to be not less than 90% of the value in ideal diffraction-limited system. the range of allowance becomes larger gradually with the increase of angle theta(n) between the normal of optical interface n and the optical axis of imaging system <^> z. if a polarization beam splitter is considered, p root d-alpha -> infinity, theta(n) /sin(-1) n a should be greater than 1-3.