Abstract: To solve the problem of calculating visible net area under any direction in infrared radiation calculation for military helicopter, a new algorithm based on stochastic simulation was proposed. By using surface modeling method, the helicopter's three-dimensional model was constructed and discretilized into quad surface elements. The mathematic model for helicopter was represented with the winged-edge structure. Visibility test, depth test and shelter test were applied to find out all the other polygons that have occultation relationship with the researched spatial polygon, then put them into a set. The statistics method of random variable was introduced subsequently to calculate the net area of this polygon. The calculation results of certain military helicopter and simple object show that the percentage error for simple object can be controlled within 5%, and for complex object can meet the engineering requirement by controlling the total polygons and random points reasonably. The algorithm has been used successfully in the calculation software of military helicopter 's infrared radiation. Applications show that the algorithm is stable, reliable and suitable for engineering analyses.