Canopy interception is the starting point of rainfall distribution in forest ecosystem, and accurate simulation of canopy interception is the basis of exploring forest hydrological process. In order to study the influence of stand density on canopy interception and the adaptability of Gash modified model in stand structure, the Acer truncatum forests with two kinds of forest density in Badaling Forest Park of Beijing were taken as the research object. The simulation analysis of the canopy interception process was carried out, and the adaptability of the Gash correction model was discussed for the stand structural characteristics of the A. truncatum forest. The results showed that: (1) In the growing season of 2013, the measured values of the throughfall, stem flow and canopy interception of A. truncatum forest with the density of 3 665 strain/km2 were 365.5 mm, 38.19 mm and 69.82 mm, and the simulated values by the modified Gash model were 386.45 mm, 33.86 mm and 53.21 mm. Compared with the measured values, the relative errors were 5.73%, 4.33% and 23.80% respectively. The throughfall, stem flow and canopy interception of A. truncatum forest with the density of 1 090 strain/km2 were 380.2 mm, 19.04 mm and 74.25 mm, and the simulated values by the modified Gash model were 368.37 mm, 13.71 mm and 91.43 mm. And the relative errors were 3.12%, 27.99% and 23.13% compared with the measured values. Under the sparse forest conditions, more rainfall penetrated the canopy and entered the next hydrological effect layer of the forest ecosystem. The simulation results of the Gash modified model also showed basically consistent characteristics. The simulation accuracy of the model to the A. truncatum forest can basically meet the needs. (2) Sensitivity analysis of six key parameters in the Gash modified model was carried out, such as the average rainfall intensity (${\bar R}$), the drainage partitioning coefficient (Pt), the canopy storage capacity (S), the canopy cover fraction per unit area (c), the trunks storage capacity (St), the average saturated canopy evaporation rate(${\bar E}$). The influence of the six parameters on the A. truncatum forest with high density was R > S > E > St > c > Pt. And it was S > R > E > C > St > Pt on the A. truncatum forest with low density. It can be concluded from the analysis that it is the key to improve the simulation accuracy of the modified Gash model by selecting the appropriate time scale to calculate the average rainfall intensity and the canopy storage capacity. Proper thinning can provide better water conditions for stand growth.
