In the high-speed cutting process, coolant is applied to ensure the cutting tools temperature stable. In the current study, scholars mainly studied the characteristics of the tool surface temperature during the cutting process. However, the cooling and heat transfer characteristics of the cooling fluid were ignored during the cutting process in their study. By analyzed the motion state of the coolant around the cutting tool, a heat transfer model of the coolant fluid is proposed in this, paper based on the fluid boundary layer theory. In the heat transfer model, the solution of the temperature gradient of the coolant is obtained by solving the Brahzyus similarity solution. Moreover, the relationship between the temperature of the cutting tool in the coolant environment and the natural convection environment was analyzed by simulation experiment. Then the temperature trend of different Pr for coolant was obtained. In addition, the effect of coolant flow on the cooling effect of the system was discussed in this paper, and the expression of Nu number was obtained. The heat transfer model about the coolant boundary layer proposed in this paper is of great significance for the study of the coolant's cooling characteristics during high speed cutting. (C) 2017 Elsevier Ltd. All rights reserved.