The unique electronic properties (electron mobility and carrier lifetime) are key factors for metal oxide semiconductor devices that directly determine the device's performance and application. Electron mobility of metal oxide semiconductor has a certain impact on response and operating temperature of gas sensor. Heterojunction composites of carbon quantum dots (CQDs) and perovskite materials have attracted much attention due to their great potential for gas sensors. In this paper, a gas sensor for monitoring methanol gas was developed based on nitrogen-doped carbon quantum dot/Ag-LaFeO3 (NCQDs/Ag-LaFeO3) p-n heterojunction materials (NALPN). NCQDS and Ag-LaFeO3 form a heterojunction, which improves the carrier transport ability and separation of electron-hole pairs. The surface of NCQDS contains -COOH, optimize the selectivity of Ag-LaFeO3 to methanol gas. Gas sensitivity test results show that the NALPN to 5 ppm methanol gas possessed high response (73), low operating temperature (92 degrees C) and good selectivity. These excellent properties prove that NALPN materials are the main competitors for future gas sensitive materials.