The reliability analysis model including two stages of life cycle was established based on bathtub curve. The parameters were estimated by the least square method. The reliability function was determined by the linear correlation coefficient and Kolmogorovsmirnov (ks) test methods and the terminal time of early failure was calculated. A theoretical basis was provided for reasonably designing of early failure test in enterprises, removing early failure, and improving products reliability. Finally, a case study of the domestic computer numerical control (CNC) with 2 years local test fault data is combined to give details in the process of calculation and analysis.