Abstract: The work clearance of the rolling bearing affects its lifetime and survivability of the transmission system greatly.In the condition of loss of lubrication,the variation of work clearance in the high speed rolling bearing of helicopter transmission system is analyzed,and the factors such as the rolling bearing's installing,turning,difference in temperature and load are researched.The formulas for work clearance variation are derived with considering the elasticity,and the numerical example is presented.They provide the bases for choosing rolling bearing parameters reasonably,improving the lifetime of bearing system and the survivability of armed helicopter transmission system.