A waveplate is used to measure the polarization effects in optical systems. For a ultrahigh numerical aperture (NA) imaging system with a large angle of incidence, the light concerned may be not parallel to the optical axis of the system, but a conical light beam with a large angle to the optical axis of the system. Therefore, the conventional double-plate type 1/4 waveplate can not be used in such systems. Instead of it, a four-plate wide-viewing-angle (WVA) 1/4 waveplate composed by positive and negative crystals can be used. The additional retardation caused by WVA 1/4 plate is analyzed in assembly angle error with three direction and two manufacturing errors. It is found that when the WVA 1/4 waveplate assembly error and the optical axis error of one piece crystal are both ±2°in the lithography system of NA of 1.35, the retardation error deduced by the latter relative to the former is above ten times. The deviation of light polarization degree (DOP) on mask level of high-NA lithographer is analyzed caused by the maximum additional retardation of WVA 1/4 waveplate, which comes from assembly and manufacturing error. As a result, It is concluded that when the retardation error is in the range of ±10°, the DOP deviation can be controlled in the scope of one in a thousand.