Hydrostatic testing is an important step in pipeline construction. This test ensures the integrity of newly-constructed pipelines. Testing pressures used by Chinese construction contractors are lower than that in foreign countries. Nowadays, higher testing pressure is considered safer for pipeline operation. But what is testing pressure we should apply? Basing on fracture mechanics theory, this paper addresses the effects of testing pressure on pipeline materials, and calculates the maximum safe testing pressure. Also, experiments validate the theoretic conclusions.