No effective method can be adopted to consider the influence of space charges when calculating the total electric field distribution in the main insulation system of the valve-side winding of converter transformer. In order to calculate total electric field in oil-paper insulation system

we put forward a new simulation method in oil-paper insulation based on a transient upstream finite element method（TUFEM）

in which the time variable is considered. The TUFEM is used to calculate the total electric field in oil-paper insulation system by considering motion law of space charges. The simulation method is verified by comparing the simulation results to the test data in references. The motion law of space charges and distribution characteristics of the electric field under difference voltage values in single-layer oil-paper insulation is obtained. The distribution of space charge in a double-layer oil paper insulation system is further studied by this method. The results show that the TUFEM has an excellent accuracy compared with test data in references. When carrier mobility is a constant

the higher the initial electric field intensity is

the less time the space charge reaching dynamic stability will take

and the greater distortion rate of internal total electric field will be. Space charges are hindered on the interface of double layers of oil-paper insulation

which can be simulated by setting an appropriate interface potential barrier.This method will promote the design and optimization level of UHVDC converter transformers.