Temperature and moisture are two key factors to affect LED reliability. The effects of temperature and moisture on the reliability are numerically investigated based on a real LED module from one company. The changes of temperature and moisture with time are given, and the distributions of thermal and moisture stresses are presented. The results demonstrate that temperature of LED module can reach steady after 1.5 minutes while its moisture field needs 46 days to reach balance. The moisture stress is in the magnitude order of 103 Pa, but the magnitude order of thermal stress is about 108 Pa, which means the moisture stress is much smaller than the thermal stress during LED operation process. The results provide the basis for LED packaging design and further study on the effect of thermal coupled with moisture on the LED reliability.