In this article, a series of novel semi-interpenetrating polymer networks (s-IPNs) based on linear polyimide (PI) and crosslinked epoxy (EP) were firstly prepared aiming at controlling violent vibration and noise originating from operation of the machine. The damping, thermal, and mechanical performances of s-IPNs films were systematically investigated in terms of the structure of polyimide (themolar ratios of diamines) and the component ratios of PI/EP. The results indicate that PI/EP s-IPNs films exhibit prominent damping properties, and the effective damping temperature range can reach up to 58.8 ℃ when molar ratio of diamines is 1:3 within PI and component ratio of PI/EP is 70:30. Meanwhile, all the PI/EP s-IPNs films show good thermal stability compared to cured EP and certain mechanical behaviors due to the formation of semi- interpenetrated structure. Meaningfully, the prepared novel PI/EP s-IPNs will be used as effective damping materials and have a potential application in damping fields.