Abstract: Overdisplacing operation often occurs in fracturing treatment in order to meet the safety requirements of tools or treatments, especially in multi-stage fracturing horizontal wells with drillable bridging plug. However, overdisplacing may affect post- frac production due to decreasing fracture conductivity, hardly any models for studying this effect. The calculation model of overdisplacing sweep region was established based on the fractureseam features and Harrington formula; the conductivity model of unpropped hydraulic fracture was established according to the fracture closure, Carman-Kozeny formula and Walsh model; moreover, the point source theory, the unstable gas seepage formula and the potential superposition theory were adopted to establish the productivity calculation model of fracturing horizontal gas wells. From the above models, a new simulation model was built to predicting the production of fractured horizontal gas wells considering overdisplacing, and a calculation example and single factor analysis were performed. The calculation results show that the larger the rock grain sizes, the higher the fracture conductivity and the smaller the overdisplacing liquid volume, the lower the production reduction. The fracture conductivity of overdisplacing sweep region plays an important role in productivity performance. Overdisplacing, once formed, will have a great effect on the productivity, however, the productivity of horizontal gas wells gradually goes down with overdisplacing volume increment, and downward margin decreases too. Thus, the models proposed could not only provide basis for a research idea for productivity of fracturing horizontal gas wells considering overdisplacing operation, but also supply guidance for the optimization design of a multi-stage fracturing horizontal wells.