Competition for light was one of the key factors for decline in peanut yield in agro-forest alley cropping systems, since lower PAR of the peanut rows and peanut yield was found in the alley cropping system than that, respectively, in the peanut mono-cropping system, and peanut yield is correlated significantly to PAR. After tree pruning in early June 2001, relative PAR index of the peanut crops was increased to 88.7% and 67.5% from 79.2% and 63.4% in May in the 5-year-old and 9-year-old Choerospondias axillaris alley cropping systems, respectively. However, with the trees growing, it was slowly decreased to 80.8% and 65.7% in the two systems in July, respectively. After tree pruning, relative peanut yield was increased to 68.2% and 58.1% in 2001 from 64.1% and 55.4% in 2000 in the two systems, relatively, which indicated that tree pruning may mitigated slightly competition for light in a short period, but it couldn't meet the demand of peanut for light during its growing period.