Noise sources characteristics of electric locomotive cabs and sound insulation performance of its all walls were studied experimentally. Based on the sound power level equivalence principle, the sound power level of outdoor noise sources was equivalent to indoor sources. Then, the sound pressure level (SPL) at measuring point in cab was predicted based on the existed empirical formulas for sound insulation designing. Results showed that the wheel/rail noise, equipment room noise, air conditioner and heater blower noise in cab were the main noise sources; Due to noise produced enough reverberation sound in the equipment room, the SPL at measuring point in the equipment room had nothing to do with distance between measuring point and noise sources; There was a certain deviation between the simulated results and measured results, but still in the acceptable range. The analysis method proposed can be utilized to predict SPL of electric locomotive cabs in the early design stage or suggest improvements.