Abstract: In order to study the influence of constraint conditions on the reaction characteristics of CL-20-based PBX explosive after non-impact ignition, a variable constraint ignition test device was designed. Combined with high-speed camera and pressure sensor, the reaction intensity, reaction pressure growth and air shock wave overpressure of CL-20-based PBX explosive under different constraints were analyzed. Furthermore, the relationship between the constraint conditions and the reactivity of explosive charge is analyzed by comparing with the peak value of complete detonation air overpressure. The results show that the non-impact ignition reaction process of CL-20-based PBX explosive under constraint conditions is divided into two stages : slow growth of reaction pressure and rapid growth of reaction pressure. With the increase of constraint strength, the distinction between the two reaction stages is gradually not obvious. The constraint conditions have a significant effect on the reactivity of explosive charge. When the shell thickness is 6mm and the strength of bursting disc is 2MPa and 50MPa, the reactivity of explosive is 0.11 and 0.14 respectively. When the shell thickness is 20 mm and the bursting strength is 2 MPa, the charge reactivity is 0.31. It can be seen that the reaction intensity of CL-20-based PBX explosive can be effectively reduced by weakening the mechanical constraint strength.