Abstract: Stability control of supports under dynamic load is one of the challenges of mining steeply dipping seam. The research object is to study the dynamic load destabilisation mechanism of the support for high cutting and steeply dipping mining working face by using field measurement, physical simulation, theoretical analysis and numerical simulation. The characteristics of typical dynamic loads on hard roof working face with thigh cutting and steeply dipping mining working face are summarized, and the destabilization mechanism of the support under the action of multi-dimensional dynamic loads is analyzed. The results show that when the periodic weighting, the high cutting and steeply dipping mining working face is easy to produce the incoming pressure dynamic load on the top beam or caving shield, when the top plate collapses, it is easy to produce the positive pressure impact type dynamic load and back push impact type dynamic load, and the collapsed gangue slip and roll is easy to cause the inter-frame (side push) dynamic load. The kinetic equations of the basic modes of motion of the support sliding and rotating and their coupling states under different influencing factors are given, and it is concluded that the support rotation (tilting tendency) and the inter-frame force increase with the decrease of the normal load of the roof plate, the increase of the tangential load of the roof plate, the increase of the degree of deflection of the roof plate and the increase of the mining height.Numerical simulation shows that under the action of positive pressure impact, the support rear column is more loaded than the front column; under the action of rear push, the bottom of the column is more loaded than the middle and upper part; when the action between frames, the upper column in the same support is more loaded than the lower part, and the upper bracket between brackets is more loaded than the lower bracket, and all have obvious asymmetric loading characteristics. Based on the findings of the study, measures such as weakening the hard top plate by overrunning periodic blasting, reducing the specific pressure of the bottom plate, installing additional bi-directional lateral pushing devices and using touch top with pressure to move the support were proposed to effectively reduce the impact of dynamic load on the stability of the support.