In order to obtain the characteristic parameters and fault influence laws required for fault diagnosis of the pantograph pneumatic system (PPS), aiming at the problem that some faults are not easy to inject or the injection cost is high, the software-based equivalent fault injection method was put forward. The composition, principle, and fault modes of PPS were introduced. Based on the equivalent fault injection test, the influence laws of five faults under different fault degrees were studied. The results show that the low air source pressure can cause the bow to rise too slowly or even be impossible. The airbag leakage will cause the airbag to charge air for too long or not reach the target pressure to trigger the lifting bow failure. When the pressure-reducing valve is set at 900 kPa, the bow lifting time is 2.7 s faster than normal. When the opening degree of the exhaust valve is 25%, the drawdown time is 1.0 s slower than that of normal. The damage to the air duct of the carbon contact strip will cause the wind pipe pressure and the airbag to drop sharply and trigger the accidental bow failure. The research results provide references for the fault diagnosis algorithm design of PPS.