Abstract: In the underground mining of the broken， irregular blocks ore body of the metal deposit，it is an important guarantee for the safe and efficient mining at the posits to study and recognize the ground pressure activity law of the stope and take effective measures to control the ground pressure activity.The Houhemushan mining area of Hemushan Iron Mine is a broken ，irregular blocks ore body mining by sublevel caving method without sill pillar.As the decline of working face and the change of stope structural parameters，large-scale ground pressure activities took place in the first sublevel of the -250 m middle section，and the footwall haulage roadway and the hanging wall drifts were seriously damaged，such as the two sides of the roadway are squeezed，broken or broken， the floor is bulging，and the roof is sinking etc.， which makes the roadway unable to be repaired，and seriously affects the safety production of the mine.Based on the analysis of the characteristics of ground pressure activity and the failure mechanism of stope，it is concluded that the ground pressure mainly comes from the wedge- shaped body pressure which is formed by the fracture and the delayed caving of rock surrounding the roof.At the same time，the mathematical model of additional stress on the wedge is established.According to the calculation results，the pressure stress at the tip of wedge is greater than the average value of the compressive strength of the ore body，which is the main reason for the rapid destruction of the hanging wall drifts，while the sliding of the fracture structural plane at the footwall of the ore body caused by the active pressure of wedge wing is the direct reason for the footwall haulage roadway destruction.According to above-mentioned analytical results，the method of controlling the slippage failure of footwall geological structural planes，depressurizing partial mining， increasing the drift interval and improving the stope support form is used to effectively control the ground pressure of wedge-shaped body and ensure the safe mining at -250 m middle section.

Key words: wedge ground pressure, inclined cracked orebody, sublevel caving method, ground pressure control of stope