Abstract: With the improvement of the cleanliness requirement of vacuum environment in semiconductor and other fields, dry twin-screw vacuum pumps are widely used due to their oil-free and high ultimate vacuum characteristics. The theoretical prediction of the pumping performance of screw vacuum pumps is realized through numerical modeling, which is the key to the research and design of screw vacuum pumps. The existing chamber model for pumping performance prediction of screw vacuum pumps has the problem of not being able to obtain the continuous pressure change curve. In this paper, a new “dynamic chamber model” is proposed for the pumping speed prediction of screw vacuum pumps. By comparing with the experimental pumping speed curves, it is verified that the new model proposed in this paper can predict the pumping speed performance of the screw vacuum pump more accurately, Verified against experimental data, it predicts more accurately: at 5.8 Pa (near ultimate vacuum), its 40.18 m³/h pumping speed shows a 31.5% deviation from measurements, versus the existing model’s 41.63 m³/h with a 63.2% deviation. Additionally, it generates continuous pressure curves for the rotor chamber, reflecting gas transport throughout the full working cycle.