This paper is the result of mineral exploration engineering. Objective Sidaogou deposit is located in the Au–Cu–W ore concentrated area of the eastern Yanbian, and is a typical quartz vein type scheelite deposit. This paper studied the property and source of the ore–forming fluids and genesis of the deposit, to promote the understanding of the quartz vein type scheelite deposit in NE China and further prospecting. Methods This paper presents the petrographic observation, microtemperature measurement and Laser Roman spectral analysis of the fluid inclusion, C–H–O isotope analysis and rare earth element compositions for the Sidaogou scheelite–quartz veins. Results Petrographic observation indicates that the liquid–rich, daughter minerals–bearing, gas–rich, and CO₂–bearing inclusions coexisted in the quartz, and all the types of fluid inclusions have similar homogenization temperatures, which indicate that they belong to boiling fluid inclusions. The lowest homogenization temperature of the gas–rich fluid inclusion (283℃) represents the ore–forming temperature. Laser Raman spectral analysis indicates that the gas phases in the fluid inclusions include H₂O and CO₂, as well as minor CH₄ and N₂. Scheelite grains yield “hump” type REE patterns with weak negative δEu anomalies. Conclusions The results indicate that the ore–forming fluids of the Sidaogou scheelite deposit are oxidizing NaCl–H₂O–CO₂±CH₄±N₂ fluids with high–medium temperature. C–H–O isotopic data indicate that the ore–forming fluids were mainly derived from magmatic water, mixed with a little bit of meteoric water, and the carbonaceous material resulted from oxidation of organic material in the sedimentary rocks from the Wudaogou Group. Therefore, Sidaogou scheelite deposit belongs to mesothermal vein type scheelite deposit, and the fluid boiling induced the precipitation of scheelite.