The limiting factors of the maximum length of horizontal wells were analyzed from the kick prevention perspective. The methods of maximum length design of horizontal sections were proposed according to the basic principles of drilling fluid dynamics and the computational model of annular pressure loss in the horizontal section. In view of the factors displacement, safe mud density window and drilling fluid rheology, sensitivity analysis of the length of horizontal sections was carried out. The results show that the maximum length of horizontal sections is influenced by displacement, safe mud density window and drilling fluid rheology. The maximum length decreases with an increase of displacement and viscosity of drilling fluid; the maximum length increases with an increase of the safe mud density window.