The Backward Monte Carlo (BMC) method is a common method for calculating the target′s infrared radiation signature because of its high accuracy and strong adaptability. Based on general CFD/IR numerical calculation method, the impact of ray discrete step size, ray number, energy carrying method on aero-engine infrared radiation intensity computation efficiency was investigated by using BMC method. The results show that the computation efficiency is high when the ratio of ray discrete step size to equivalent diameter of nozzle exit is between 0.05 to 0.1 and ray′s number is more than 105; the computation time can be shortened by dozens of times through ray carrying multiple bands energy method; the computation time of BMC method can be reduced further by parallel computation with MPI platform, but the parallel efficiently will be decreased with increasing the computation core number. In the premise of ensuring the accuracy of the results, the efficiency of infrared radiation computation was improved by reasonable selection of parameters, algorithm improvement and parallel computation.