In order to obtain the information of blasting rock size under different geostresses and avoid the phenomenon of excessive rock size after blasting in vertical shaft forward blasting expansion, a vertical shaft calculation model was established by ANSYS/LS-DYNA, the distribution law of rock debris area was studied, and the formation effects of different types of fracture surfaces were analyzed. Finally, the stress state of the rock mass was analyzed, the formation effect of the corresponding fracture surface was determined, and the formation position of the large rock was clarified. On this basis, the blasting scheme design suggestions were put forward. The results show that with the continuous increase of in-situ stress, the distribution interval of debris area becomes wider, and the main distribution interval gradually transitions from 0 ~ 300 cm² to 300 ~ 900 cm², and the rock block develops to an irregular body after blasting. When the local stress exceeds 5 MPa, the blasting will produce 1 500 ~ 1 800 cm² debris, which is close to the allowed maximum debris area of 1 736 cm², and the generated blasting rocks may block the pilot well. The vertical stress at the bottom of the rock mass close to the design excavation surface is large, the formation of horizontal fracture surface is blocked, and the blasting is easy to produce large rocks. The vertical stress of the rock mass near the upper surface of the excavated rock mass is small, and the horizontal fracture surface is easy to form. It is concluded that when designing the scheme of vertical shaft blasting expansion, it should be considered to strengthen the charge at the bottom of the rock mass close to the design excavation surface, and according to the order from the upper to the lower part of the expanded rock mass, detonate the explosives of the same charge height in turn, change the stress state of the rock mass, reduce the rock mass degree after blasting, and avoid the blockage of the pilot well by the exploded rock block.