Tectonically, Longgang Volcanic Group is located on the northeastern margin of the Sino-Korean Craton and is controlled by the Kuandian–Longgang–Dunhua deep fracture. The Dayishan Volcano in Huinan County, Jilin Province, is a typical representative of the Quaternary volcanoes on the western part of the Longgang Volcanic Group. The eruption types of the Dayishan Volcano have the stage characteristics, that is, the eruptions in the first, second and fourth stages are magmatic eruptions, while the eruption in the third stage is a weak phreatomagmatic eruption. Its chair-shaped volcanic cone is composed of pyroclastic fall deposits from multi-stage magmatic eruptions and pyroclastic fall rhythmic layers of weak phreatomagmatic eruptions. Based on the strata and petrography of the pyroclastic deposits of Dayishan Volcano, the particle size distribution, particle shape and fractal characteristics of pyroclasts was quantitatively studied from the perspectives of particle size-shape analysis and fractal theory. The particle size distributions of the Dayishan pyroclasts are all unimodal, mainly showing a coarse-grain dominance. The peak value of the particle size distribution of the weak phreatomagmatic pyroclasts in the third stage is significantly smaller than those in other stages. In terms of particle shapes, as the eruptive intensity decreases, the pyroclast shapes tend to be more irregular. However, the particle shape values of the pyroclasts in the third stage of the Dayishan Volcano are all higher than those in the other stages, indicating that the eruption products in the third stage significantly approach a regular shape. The distribution characteristics of the Dayishan particles were fitted using the multi-segment power-law method. It was found that there are four significant fractal intervals in the particle size distribution of airfall pyroclasts of magmatic eruptions, while there are three fractal intervals in the one of weak phreatomagmatic eruption. This indicates that the formation of airfall pyroclasts of magmatic eruptions is mainly affected by the initial fragmentation of magma, high-energy secondary fragmentation and wind transportation. In addition to the effects of the above factors, the pyroclast of weak phreatomagmatic eruption is also related to the explosion caused by the steam forming from the contact between magma and water.