Gravitational waves (GWs) are ripples in spacetime caused by most violent and energetic processes in the universe, such as the rapid motion of massive celestial bodies. The GWs carry energy when they propagate through the universe. The detection of GWs holds significance for advancing human understanding of the nature and driving scientific and technological progress. The continual upgrading and optimizing of GW detectors offer novel avenues for cosmic measurements. However, ground-based GW detectors based on a large interferometer necessitate addressing various noises which are harmful to the sensitivity of the GW detectors. Among these noises, the noise from residual gas in the light beam of the interferometer is a crucial factor to affect the sensitivity. Consequently, it is necessary to establish a vacuum system to shield the laser interferometer from the effects of gas flow. This paper focuses on China’s third-generation ground-based GWs detector, conducting theoretical analysis of the influence of residual gas noise on both a 20-meter arm-length prototype and a full-scale device with a 10-kilometer arm-length. In this paper, a theoretical model for the residual gas particles passing through the laser beam is established and the effect on the beam phase is analyzed. The theoretical simulations are performed to discover the relations between the residual gas noise and significant parameters such as gas pressure of the vacuum system, temperature, mass of residual gas particles, polarization rate of the residual gas, and the curvature radius of the test mass. The simulations indicate that when the residual gas pressure is below 2×10 ^–6Pa, the GW detector can achieve the enough sensitivity, 10 ^–24Hz ^–1/2, in a frequency range from 10 to 10 ³Hz. The findings of this research offer crucial theoretical insights for designing and constructing the vacuum systems in future third-generation GWs detector prototypes and full-scale devices.