Since built-in pressure testing instrument adopting internal triggering method is susceptible to electromagnetic interference in artillery gun pressure testing, thus affecting testing precision of pressure testing instrument. In this paper, an electromagnetic shielding design was presented based on built-in pressure testing instrument. Through theoretical analysis and calculation of electromagnetic shielding, a useful shielding shell mode of the built-in pressure testing instrument, was designed and the shielding material was determined. Also, Ansoft Maxwell software was used to conduct electromagnetic simulation for shell shield design. The simulation results verify rationality of the design, a feasible scheme is provided to solve the problem of electromagnetic shielding of built-in pressure testing instrument.