High power testing methods for HV DC circuit breaker (DCCB) were investigated. Short circuit breaking tests using quasi-DC current were performed for DCCB based on the current oscillation scheme with active current injection. This DCCB has a high voltage vacuum circuit breaker as the interrupter unit. The tests were performed using two kinds of testing method (power frequency current peak method and charged reactor method) which have different breaking current waveforms. Interruption performance evaluated with the results obtained from each of the two kinds of testing method. In results, the interruption performance evaluated from these two testing method was same. Moreover, the effect of saturable reactors to the prototype DCCB was investigated in order to improve the DC current interruption performance. Due to the effect of the saturable reactors, di/dt at current zero could be decreased which makes it possible to minimize the parallel capacitance and inductance.