Preheating phase of steam assisted gravity drainage（SAGD）has direct effect on its early production response and corresponding performance in heavy oil reservoirs. Therefore，it is important to develop an effective method to improve SAGD performance. A pilot test of the fast and uniform start-up enhancement technology（FUSE）was taken as a case study.The high pressure dilation mechanism of the FUSE was revealed and its related operating pressure was optimized by using numerical simulation method. The results show that a zone with high porosity，high permeability and high water cut was formed between the injector and producer，and the heat convection between steam and reservoir rocks was enhanced，and thus the heat exchange rate and thermal connectivity between double horizontal wells were improved. There was an optimal operating pressure for the FUSE and it was closely related to the in-situ stress and the rock deformation characteristics.Field production data was applied to analyze the performance of the FUSE. The result presents that the number of days for preheating and the steam consumption in the preheating phase are reduced significantly，and the SAGD performance in the early production stage is improved obviously. It has important guiding significance for the realization of efficient SAGD development.