In the high speed precision machine tools, the thermal deformation of spindle had an important influence in machining accuracy. The data of thermal deformation of spindle was got through measuring test rod in the experiment. However, the system error existing of test rod in running and heat imported led to the difference between the measured values and the actual values. The paper has discussed the deformation of test rod caused by centrifugal force in high speed, Non-uniform thermal field in a stable state, and gravity and the variational elastic modulus. Through analyzing those factors, the main ones and neglectable ones could be confirmed, which laid the theoretical foundation in order to eliminate the interference factors in the measurement values.