Abstract: On the basis of references [1,2], in which helium was used as the coolant, this paper investigates the problem of transpiration control using water as the coolant. At its boiling point, water will be vaporized and absorb heat, so there exists heat sink in protection layer. By means of the method of imaginary node, the difference equitions with inner discontinuity are derived and the tridiagonal system of equations are obtained. When the control parameter mL is given as the series type of temperature, the result of the closed-loop control simulations show that it can control the temperature of the heat protection layer very effectively.