The invention discloses a forming method for a 35 KV and below potential transformer with a low partial discharge level, and belongs to the technical field of electrical manufacturing and power equipment. According to the forming method, before casting, a casting device is filled with a certain amount of SF6 gas, so that air gap can be reduced and partial discharge property of a product can be improved; during the casting process, a variable casting process is adopted at time intervals of 20-50 s after casting for 1-3 min every time, so that residual air in the material and the device can be removed effectively and electric properties of the product are improved; during a curing process, a stepped heating method is adopted so that the temperature is raised slowly and reaction speed can be controlled relatively smooth; and during a cooling process, a stepped cooling method is adopted so that both internal and external crack of the product which are caused by sudden cooling can be effectively prevented and a curing effect of the product can be improved. Experiments demonstrate that the potential transformer manufactured by the method of the invention has high qualified rate and good partial discharge property; and a partial discharge amount at 1.2 Um (48.6kV) is equal to or smaller than 10 pC.