[Objective] The effects of forest canopy type on water quality of rainfall with different pH values were studied in order to provide a basis for studying the effects of acid rainfall on forest ecosystems in the Huoditang forest area of the Qinling Mountains. [Methods] A self-made artificial rainfall device was used to simulate rainfall on three main forest types (Pinus tabuliformis，Pinus armandii, and Quercus aliena var. acuteserrata). Changes in the concentration of rainwater chemicals in the canopy of each forest were analyzed by rainfall time and rainfall acidity. [Results] ① The concentrations of NH₄⁺, NO₃^-, K⁺， Ca²⁺， Mg²⁺, Pb, Zn, and Cd in the throughfall of the three forests canopies reached peak values after 10—20 minutes, and the concentration decreased and stabilized after 20—30 min of rainfall. The concentrations generally increased first, and then decreased and tended to be stable with the extension of rainfall time. ② The different leaf tissue characteristics of the conifer forest and the broadleaved forest affected the leaching amount of chemicals in forest canopies. With the same pH value, the concentrations of NH₄⁺, NO₃^-, K⁺， Ca²⁺， Mg²⁺, Pb, Zn, and Cd in the throughfall were higher in P. tabuleformis and P. armandii than in Q. acuminata. ③ Acid rain can promote the loss of chemicals in forest canopies. For the same tree species, with different pH values of leaching rain, the concentrations of NH₄⁺, K⁺， Ca²⁺， Mg²⁺, Pb, and Cd in canopy throughfall and the variation range of their concentrations generally followed the order of pH_4.0 > pH_5.0 > pH_7.0. [Conclusion] According to the dynamic change process of chemical substance concentration of canopy throughfall with rainfall time, the impact process of canopy on throughfall water quality can be divided into two stages: rainfall washing (rainfall of about 10—20 minutes) and rainfall leaching (rain starts to 10 or 20 minutes later). In the rainfall washing stage, the canopy has a great influence on the water quality.