By the half-analytic calculation method, the paper analyzed the tunnel circumjacent constringency and vault settlement with time and alteration depth of tunnel face, the relevant constringency model was built, and the reasonable second support time for hard and soft rock tunnel were proposed. With the engineering case, the least-squares fitting calculation was made on circumjacent constringency of Ⅱ、Ⅲ、Ⅳ、Ⅴ grade of rocks, and the reasonable support time for these 4 grades of rock were obtained.