An in-situ water injection test across Xi’ an ground fissures has been done, in order to simulate the activity of the fissures after water seeps, from October to December, 2005. According to the settlement observed of the bottom of testing pit, it is proven that the surface water seepage speeds the movement of ground fissures. Usually, the soil on the hanging wall of the fissures is more fragmentized than that on the footwall, which is propitious to water seepage. The seepage promotes the interaction between water and soil particles and brings about the differential settlement of two sides of fissures. Therefore, surface water seepage accelerates the activity of the ground fissures.