The one-dimensional analysis has been performed using the analysis program for the flow of the propellant and the wall temperature of Laval nozzles. The material of the nozzles is A5056 and the propellant is water. In the case that the diameter of the nozzle inlet is 0.6 mm, the diameter of the throat is 0.1 mm, the mass flow rate of the propellant is 1 g/min, the inlet temperature of the propellant and wall are 500 K, Outlet pressure of the propellant is 400 Pa, the radial thickness of the nozzle is 2 mm, and the length of the divergent nozzle is 36 mm, the 151 s of the specific impulse has been achieved whereas the specific impulse with an adiabatically change is 137 s.