Abstract: The gas filter of the synchrotron radiation vacuum ultraviolet beamline absorbs the high harmonics by filling argon gas, which can effectively eliminate the influence of high harmonics on the experiment. However, due to the severe gas beam effect, the vacuum degree of the C-7 chamber is low, which is not conducive to the long-term normal use of the beamline. It is necessary to take certain measures to solve the beam effect. First of all, the paper used Molflow+ software to carry out the vacuum simulation of the original structure of the gas filter. The simulation result and experimental result are highly consistent. And the reason for the generation of the gas beam effect is further explained by the information on the angular distribution of the gas molecules. The structure of the differential hole T-4 was then optimized by changing the original rectangular hole structure to structure 2. When θ is 4°, the proportion of small-angle particles at the outlet of differential hole T-4 decreases by 16.3%, the pressure of the C-7 chamber and outlet plane decreases by 13.6% and 15.4%.