Abstract: Fracturing treatment is an important measure to economically develop and stimulate low permeability gas reservoirs and post - frac productivity is a major basis for optimized design of fracturing program. In consideration of the common influences of start - up pressure gradient on gas percolation, a productivity simulator is built for fractured gas wells, its numerical computation module is given, and simulation software for fractured gas wells with start - up pressure gradient considered is programmed. Calculation with real data shows that start - up pressure gradient has great influences on productivity of fractured gas wells, therefore the effects of start- up pressure gradient should be took into consideration when performing productivity simulation.