Abstract: In order to meet the requirements of transport capacity, Chengdu Railway Bureau plans to increase the operating speed of some existing railways, i.e., the speed of the Dachuan-Chengdu railway will be increased from 160 km/h to 200 km/h, and the speed of the Suining-Chengdu railway will be increased from 160 km/h and 200 km/h to 250 km/h. To ensure passenger comfort requirements after the speed-up, a single dimensional characteristic curve method was used to calculate transient pressure inside the train running in the tunnels, and the results were compared with domestic standards to select the vehicle type and verify the proposed speed. The results show that: considering the comfort standard, a CRH2 is recommended as the passenger train, allowing the operation speed of the Dachuan-Chengdu railway and the Suining-Chengdu railway to increase to 200 km/h and 220 km/h respectively; the single-track tunnel plays a controlling roll in the railway speed increase because of its small clearance area, and the passing of two trains should be avoided in the double-track tunnels to minimize the possibility of exceeding the transient pressure standard; in addition to the effects of operation speed and sectional area, more attention should be paid to the sealing property of trains regarding the speed-increase plans, and the principle of “independent dimensioning of every tunnel” should be maintained.