The invention discloses a nuclear power plant volume control box deoxidization testing system and method. The nuclear power plant volume control box deoxidization testing system comprises a top charging and bottom discharging system, a purging system, an oxygen content adjusting system, a temperature control system and a parameter monitoring system. The nuclear power plant volume control box deoxidization testing system provides functions of upper charging and bottom discharging flow control, temperature adjustment, oxygen content control, nitrogen supply, gas discharging and the like, and based on the functions, achieves a testing mode with intermittent purging and pressured air exhausting. The invention also designs corresponding testing methods for different working conditions and helpsacquire rules of influence of volume control box liquid level, waiting time and purging time on intermittent purging deoxidization effects as well as the rules of influence of standing time on pressurized air exhausting deoxidization effects; by comparing the testing data of two methods, difference of intermittent purging and pressured air exhausting in deoxidization effects can be acquired to provided optimized data support for optimization and adjustment of deoxidization strategies of actual generator units.