Based on the study of the Tertiary igneous rocks and the related reservoirs of the Huimin d epression, this paper comprehensively analyzes the relation between the lacu strine volcanism and the forming of hydrocarbon reservoirs. Huimin depression is a rift lacustrine basin with abundant igneous rocks. The volcanic activity le ad to the palaeogeothermal rise, thus accelerating the transformation of org anic matter into hydrocarbon in the igneous rock area when the volca ni c activity occurred before the formation of hydrocarbon. During the diagenetic s tage of the igneous rocks, the reservoir space can be formed. Ac cording to the forming mechanism, the reservoir space can be divided into primary pores, solution pores, structural fractures, shrinkage fractures etc. A ser ies of traps such as igneousscreened trap, volcanic conedrape trap, intrusiv e rock lithologic trap and so on can be formed with the magma intrusion and erupti on. In brief, the volcanism plays a positive role in the trap formation and h ydrocarbon generation in the Huimin depression.