Abstract: In order to solve the problem of parasitic coupling that prevents the designed filter response from converging to the design target when designing microstrip split-loop resonator filters using space mapping method, a two-step optimization strategy is proposed in this paper. During the iterative design process using the space mapping method, the parasitic coupling is incorporated into the target matrix through the modification of the target coupling matrix to complete the design of filter. The effectiveness of this method has been validated by taking a six-order microstrip split-loop filter with coupling structure as an example. This method can effectively reduce the number of full-size electromagnetic simulation of the filter and improve the design efficiency.