Abstract: Electromagnetic reverberation chambers are typically calibrated for characteristic parameters such as field uniformity and normalized field strength under low input power conditions. However, in practical applications like electromagnetic compatibility immunity testing, these chambers operate under high input power conditions. Currently, relevant international and domestic standards ignore this difference, providing no specific theoretical or experimental evidence. This paper presents a designed experimental study to investigate the influence of input power on the characteristic parameters of electromagnetic reverberation chambers. A rapid calibration technique using 3D photoelectric field probes was employed for low input power calibration, while high input power parameter measurements were conducted under conditions consistent with actual automotive component immunity tests. Results show that the impact of different input power levels on field uniformity is generally within ±0.5 dB, and the effect on normalized field strength is within 2 dB. Based on these findings, recommendations are provided for calibrating field uniformity and normalized field strength during electromagnetic reverberation chamber calibration and testing processes.