Abstract: In order to provide a theoretical basis for running speed-up trains on single-track railways in China, an analysis is made of the influence of running speed-up trains on the carrying capacity on speed-up single-track lines. A calculating model for speed-up trains coefficient of deduction is developed. Through numeric analysis and simulation, an important conclusion is drawn out that the passenger trains coefficient of deduction on single-track lines decreases with the increase of running speed. Through analysis of the relationship between the numbers of passing and overtaking behaviors of speed-up trains on single-track lines, a reasonable quantity of speed-up trains to run on single-track lines is worked out, and a general conclusion about the influenceof thequantity and running speed of the speed-up trains on the travelling speed of freight trains on single-track lines is made.