Abstract: The effect of high temperature on protective enzyme activity of Larix principis-rupprechtii is studied to provide a basis for seedling cultivation and forest conservation. We set 4 treatments as W1 (25℃ control), W2 (30℃), W3 (35℃), W4 (40℃), and set the duration of the temperature treatment as 1, 3, 5, 7, 9, 11 h. The results showed that: the SOD activity of leaves under W4 was significantly higher than that of control after 5 h; the SOD activity of stems under W2, W3 and W4 treatments were significantly different with that of control after 5 h, at the same time, the SOD activity of stems under the 3 treatments were lower than that of control by 12.61%, 1.93%, 26.64% after 11 h; the SOD activity of roots under W2, W3, W4 treatments were significantly higher than that of control after 5, 7 h, and, the SOD activity of roots under the 3 treatments was lower than that of control by 8.35%, 5.99%, 28.47% after 11 h; the POD activity of leaves under W4 was higher than that of control by 109.75%, 20.11% after 3,5 h and the difference was significant; the POD activity of stems under W3 was higher than that of control by 40.16% after 11 h and the difference was significant; the POD activity of roots under W4 reached the highest value after 5 h. The high temperature duration above 35℃ should not exceed 5 h for Larix principis-rupprechtii.