Abstract: When adopting horizontal well to exploit bottom water and gas cap reservoir, water and gas will inevitably cone into it. This is an obstacle to the development of the horizontal well technique. In this paper, studied water and gas coning mechanism in horizontal well, put forward a theory of avoiding water and gas from coning during exploiting bottom water and gas cap reservoir with horizontal well. Based on the theory, put forward several technologies of avoiding water and gas from coning. This paper not only demonstrated the feasibility of the theory and the technologies, but also derived reservoir engineering calculation formula of bottom water reservolr based on the theory by use of superposition principle.