Industrial oil and gas have been found in the volcaniclastic rocks of the Huoshiling Formation erupted underwater in the continental lacustrine basin of the Changling fault depression in the Songliao Basin, which has broad exploration prospects. The study focuses on the reservoir space characteristics, physical properties and pore structure differences of the underwater eruption pyroclastic rock reservoirs in the Huoshiling Formation, and analyzes the reasons for the differences in physical properties of different types of reservoirs and their formation and evolution processes. There are mainly the following four aspects: ① Tuff, with its high volcanic glass content, predominantly features devitrification and dissolution pores as its main reservoir spaces. Coarser particle sizes in tuff correlate with improved physical properties, including larger and more abundant pores. Sedimentary tuff, rich in clay minerals, exhibits mainly interstitial spaces between these minerals and poorer physical properties. Tuffaceous sandstone, with high levels of soluble components like feldspar, debris, and laumontite, is characterized by dissolution pores. ② The average porosity is 2.43%, and the average permeability is 0.076×10^-3 μm². Coarse-grained tuff exhibits the highest porosity, followed by tuffaceous sandstone and fine-grained tuff, with sedimentary tuff displaying the poorest physical properties. ③ Devitrification significantly contributes to the high porosity yet ultra-low permeability observed in tuff reservoirs. Organic acid dissolution during the middle diagenesis stage, resulting from two separate oil and gas fillings, further enhances porosity. Additionally, fractures serve as conduits for organic acids and deep hydrothermal fluids, promoting further dissolution that connects dispersed dissolution pores and enhances reservoir space effectiveness. ④The coarse-grained tuff reservoir in the near-source facies gas-carrying subaqueous pyroclastic flow subfacies is a favorable target for oil and gas exploration.