Considering adverse effects of shallow gas geology on Hangzhou Metro construction, based on the fluid-solid coupling analytical method of multi-phase media, effects of shallow gas on diaphragm wall trenching construction were examined by using FLAC-2D software. In combination with the diaphragm works of a typical subway station in the region buried shallow gas, the deformation on slurry trench of diaphragm wall were analyzed under working conditions using different specific gravity slurry. Results show that shallow gas escape of the stratum significantly affects stability of the groove wall, easily leading to collapse of the soil and resulting in the concrete diaphragm wall with quality problems such as honeycomb, reducing diameter, bulging, breaking zone and etc. In trenching construction of the diaphragm wall, increasing the specific gravity of slurry appropriately is an effective way to reduce adverse effects of the shallow gas, but it should not be too large. A suitable range of mud weight varies from 1.06 to 1.10.