The open hole gravel packing completion technology is the main technical means used for sand control production in deepwater gas wells. However, in actual field operations, due to problems such as loose reservoirs, long horizontal well sections, and narrow operation windows in deepwater gas fields, gravel packing sand control operations often end in failure. By finely depicting the pressure distribution regular of each stage, a whole process gravel packing pressure calculation model was established, and a alternative path screen calculation model was supplemented. The influence of key operating parameters on the gravel packing process was analyzed, and the accuracy of this method was verified by comparing with the actual downhole monitoring data of deep water gas well. The results shows that with the increase of pump rate, the filling pressure of α and β wave increased, and the sand to mass ratio gradually decrease. However, the frictional pressure formed in the sand bridge and transmission pipe in the alternative path screen increase rapidly, with a growth rate significantly greater than that of the flushing and screening annulus. The larger the flushing ratio, the greater the flow resistance in the flushing annulus. The optimal design flushing ratio is 0.70~0.83. Compared with the real-time monitoring pressure data of the tubing strings during each stage of the gravel packing operation, the theoretical calculation and actual monitoring pressure values have an error of only 2.1 %, and the final gravel packing efficiency of the well reaches 138%. It provides good technical support for the gravel packing operation in deepwater gas wells from both theoretical and engineering applications, and can provide technical guidance for similar deepwater horizontal well gravel packing operations in the future.