Convective-type boundary conditions at interface of vessel walls are used in simulating convective heat transfer in blood vessels. To study feasibility of the method, convective heat transfer between blood and tissue in a simple furcated vessel system is computed with finite element analysis. Mean Nusselt number on cross-section along the vessel is obtained at various flow velocities or vessel radii. It shows that the mean Nueselt number in the branching vessel varies within a narrow range, and shows fast convergence rate. A tongue with a simple vascular tree is simulated as an example. Conjugated numerical method, and a approximate method are used to calculate 3-D velocity and temperature of the tongue. Distributions of temperature calculated are similar and quantitative difference between temperatures obtained by two methods is less than 0.2℃.