Abstract: The litter decomposition rates of pure and mixed forest of poplar and black locust are studied in this paper．The results show that the litter decomposition rate increases with the soil moisture increasing ．The litter decomposition rate under maxinlurn moisture capacity reveals the fastest．The initial decomposition rate is the biggest under the condition of 70％ field moisture capacity，it needs four days to get the big est decomposition rate while the others need seven days．The order of the litter decomposition rate is pure black locust>mixed forest>pure poplar．It is considered that C／N in pure black locust litter is substantially higher than that in pure poplar litter．It can reduce the C／N ratio and accelerate the litter decomposition by mixing poplar with black locust．