By the phase field approach, the dendritic growth in binary alloy melt was simulated respectively using two types of temperature boundary conditions, i.e., the constant temperature boundary by which the boundary temperature was fixed at the initial temperature, and Zero Neumann temperature boundary. The influences of the temperature boundary conditions on numerical results are investigated. How to choose appropriate temperature boundary conditions is proposed. The results show that: 1) when the computation region is limited to a changeless size, the Zero Neumann and constant temperature boundary conditions lead to the different dendritic growth behaviors, and the Zero Neumann condition is preferable to the constant temperature condition; 2) when the computation region is enlarged continually with the computational time according to the increasing thermal diffusion scale, the two types of temperature boundary conditions achieve the consistent tip velocities and tip radii, and they both are appropriate choices. By the phase field approach, the dendritic growth in binary alloys melt was simulated respectively using two types of temperature boundary conditions, ie, the constant temperature boundary by which the boundary temperature was fixed at the initial temperature, and Zero Neumann temperature boundary. The results show that: 1) when the computation region is limited to a changeless size, the Zero Neumann and constant temperature boundary conditions lead to the different dendritic growth behaviors, and the Zero Neumann condition is preferred to the constant temperature condition; 2) when the computation region is enlarged continually with the computational time according to the increasing thermal diffusion scale, the two types of temperature boundary conditions achieve the consistent tip velocities and tip radii, and they b oth are appropriate choices.