A new Stokes polarimeter for high accuracy measurement of solar magnetic field is being developed by National Astronomical Observatories, Chinese Academy of Sciences (NAOC). This instrument will be installed in the Space Solar Telescope (SST), which has a one-meter primary mirror, and a two-dimensional spectrograph with 8-channel birefringent filter. In order to minimize the crosstalk in linear polarization from the circular polarization, a novel optical assembly has been selected. This design consists of a quarter retarder, a rotatable polarizer, and a half retarder. The half retarder will rotate with the polarizer by an angle of half quantity of the rotating angle of the polarizer. In this paper, we will introduce this polarimeter and discuss the achromatic performance of the polarization elements in the polarimeter. We will focus on comparing the orientation and retardation of different kind of achromatic waveplate in profiles and give which is the best one for SST polarimeter. In addition, we will show the calculation crosstalk value of this polarimeter at designed wavelength.