A fiber optic rotary joint loss analysis method based on virtual prototype was proposed. The input-output equations of light in dove prism are derived. A hybrid architecture based on ray tracing model and analytical model was employed in a homogeneous coordinate system;the angle and position deviations of collimating lens and dove prism were considered as input error in the model as well as bearing clearance and gear precision. 30 000 random samples, of which angle precision is ±100″ and position precision is ±0.01 mm, were studied. The result shows that angle error of dove prism and collimating lens must be ±1′ or less while the maximum loss is required less than 4dB, the distribution of loss P(X>3 dB) is required less than 0.5%.