In order to analyze the mechanism of shock sensitivity of CL-20/HMX cocrystal close to that of HMX， ReaxFF molecular dynamics simulation was used to investigate the mechanical-thermal structural changes and subsequent initial chemical reactions in CL-20/HMX cocrystals with or without voids. The structural deformation and subsequent chemical reaction process are effectively analyzed by using the momentum mirror model combined with shock-front absorbing boundary condition. When shocks subjected to CL-20， HMX， and CL-20/HMX， it is found that the decomposition speed of CL-20 is faster than that of HMX， while CL-20/HMX"s decomposition speed is very close to HMX"s. Besides， the decomposition speed of CL-20/HMX ［100］ shocks is faster than ［111］ shocks. This phenomenon is related to alternative arrangement of CL-20 and HMX molecular layers and the relative slip amount. When CL-20/HMX with 20 nm diameter void is shocked along the ［100］ direction at particle velocity of 2 km·s^-1， hydrodynamic jet collapse does not occur instead of viscoplastic pore collapse. It largely promotes the rapid decomposition of CL-20 and HMX molecules in the high temperature and high pressure conditions formed by pore collapse and the viscoplastic deformation of crystal structure. A new hot spot formation from the void collapse further enhances the shock loading process.