The Wide Field Survey Telescope (WFST) is a 2.5 m optical telescope that has been in operation since 2023 September. Located on Saishiteng Mountain in Qinghai Province, the WFST benefits from exceptional atmospheric seeing conditions. However, the effect of the existing telescope dome on the astronomical seeing of WFST has not been characterized, which inevitably affects the imaging performance of the telescope. Two differential image motion monitors of the same configuration, one located in the dome and the other outside the dome, were used for seeing monitoring during the maintenance period of the WFST. Astronomical seeing measurements were conducted simultaneously inside and outside the dome under different dome ventilation configurations to quantify their effects. Statistical analysis of the seeing data collected under different ventilation conditions indicates that proper air convection in the dome can improve the in-dome seeing to reach near the level of the out-dome seeing and thereby improve the image quality of the WFST.