Loads on a gearbox casing of a certain type of tracked vehicle were calculated according to the engine’s full load characteristic curve and the worst load condition where the gearbox operated while the tracked vehicle was running,and then stiffness and strength of the casing were analyzed by means of Patran/Nastran software.After analysis,it was found that the casing satisfied the Mises’ yield condition;however,the stress distribution was heterogeneous,and stresses near the bearing saddle bores of the casing were higher while those in other regions were much less than the allowable stress.For this reason,thicknesses of the casing wall on bearing assembling holes needed increasing,while those in other places can decrease.After much structural improving and re-analysis,the optimal casing design was found,and its weight decreased by 5%;the casing still satisfied the Mises yield criterion and the stress distribution was more homogeneous. Loads on a gearbox casing of a certain type of tracked vehicle were based on the engine’s full load characteristic curve and the worst load condition where the gearbox operated while the stiffness and strength of the casing analyzed by means of Patran / Nastran software. After analysis, it was found that the casing satisfied the Mises’ yield condition; however, the stress distribution was heterogeneous, and stresses near the bearing saddle bores of the casing were higher among those in other regions were much less than the allowable stress.For this reason, thicknesses of the casing walls on bearing assembling holes needed increasing, while those in other places can decrease.After much structural improving and re-analysis, the optimal casing design found, and its weight decreased by 5%; the casing still satisfied the Mises yield criterion and the stress distribution was more homogeneous.