Bullet impact tests for four different sizes （Φ100 mm×45 mm（1^#），Φ50 mm×100 mm（2^#），Φ75 mm×150 mm（3^#） and Φ100 mm×200 mm（4^#）） PBX-2 explosives were carried out by improving test method. The time of bullet perforating target and velocity after perforating target were obtained. The reaction overpressure for different size explosives were measured. The reaction properties for different size PBX-2 explosives were analyzed in bullet impact test. Results show that the reaction of PBX-2 explosive is more violent with longer size. The numerical simulation of bullet impact test for 1^#, 2^# and 4^# samples was completed by ANSYS/LS-DYNA, and the calculated results are in accord with test results.