Abstract: The waterholding properties of canopy of Sapindus mukorossi plantation with different DBH （diameter at breast height） were measured to analyze the dehydration rate of different part fuel, and do quantitative analysis of fireproof effect of canopy. The results showed that, in Sapindus mukorossi plantation, canopy′s waterholding properties had significant differences in different DBH stands. When the DBH of Sapindus mukorossi plantation was 20cm, moisture content of canopy reached maximum. In the process of fresh branches drying, the relationship of branch′s weight and drying time was exponential regression, and branch′s water loss rate and drying time showed binominal regression relationship. In the first 6h, the weight of all treated branches was decreased with drying time continuing. After 6h, the value tended to be stable. After 8h, the weight of branches and water loss rate had no change anymore. In the upper and middle portion of plantation canopy, those branches with 15cm DBH showed the highest water loss rate, while in the below portion, those with 10cm DBH reached were highest.