Abstract: For the safety of gas transmission in long distance pipeline, the method regarding how to get the proper value of pressure drop rate for the fast block valve on pipeline is studied. The finite element method is used to solve the partial differential equations for the transient flow problem. And both steady and transient flow models are used to simulate the pipe flow when the leakage is occurred suddenly. Then the practical set up value of pressure drop rate are calculated. The detail algorithm is derived in the paper and several examples are calculated using the generated software.