Abstract: The paper reviews the development course of inheritance and innovation of mining under pressure, expounds the concept and the necessary and sufficient conditions of mining under pressure, and on the basis of the connotation of mining under pressure, the base level of erosion is defined as the boundary(interface) of shallow and deep mining under pressure. The paper clarified that mining above confined water is mining under pressure, while mining under aquifer does not belong to the category, and corrects the improper expression of roof and floor pressure in "Coal Mine Safety Regulations". This paper summarizes the theory and technology directly serving the mining under pressure, the three technologies of exploration, prevention and protection, the three theories of mechanism(disaster mechanism), evaluation(risk evaluation) and prediction(disaster prediction), which constitute the theoretical and technical system of mining under pressure. The development of Ordovician karst in North China coalfield weakens with the increase of depth. It can be inferred that the deep karst runoff belt in space is mostly formed in the palaeo-karst system, while the modern karst runoff belt is developed in the modern karst. The damage fractures in the deep aquifuge increase, which lays a material foundation for the rise of confined water after mining. This paper summarizes and compares the characteristics of karst water damage in shallow and deep floor, and clarifies the mechanism of deep Ordovician limestone water inrush, the permeability, dilatancy, fracturing along the fracture, and continuously rise through the transfer of thin limestone, thus forming a large area of divergent flow. It is theoretically explained that the water inrush coefficient is no longer applicable to the case that the thickness of the aquifuge exceeds 80 m, and an evaluation method of mining under pressure of thick and extremely thick aquifuge is proposed:p₀ > 3σ₃-σ₁-p_p+s_T. According to the thickness of the aquifuge, the height of the floor damage zone as well as the height of fracturing belt of the Ordovician limestone, and the water inrush coefficient, the floor is divided into five types of aquifuge, and the corresponding five levels of mining under pressure conditions and five treatment modes are put forward. Aiming at the complex conditions of deep mining under pressure, the paper advocates the application of "whole time-space" comprehensive water damage prevention ideas and technologies. Facing the future, the constitutive model of geological body + water flow is still the biggest problem to be overcome by the academic circle. Realistic problems of stranglehold, such as the development of deep karst, fine exploration technology, water damage mechanism and evaluation prediction, and comprehensive treatment technology, are the keys to realize the safe mining under pressure.