Master equations of density operators can be concisely solved by virtue of thermo entangled state representation and t he technique of integration within an ordered product of operators.The solution of master equations of density operators is given.We get the Wigner function evolution formula in phase space and photon number distribution formula of the state, which is a superposition of vacuum state and single-photon state initially in laser process.By numerical calculation we plot its Wigner function and photon number distributi on evolution curves,when cavity gain constant and cavity loss constant are both equal to cert ain values.The effect of decoherence on nonclassical property of the state is discussed by comparing n egative area size and the depth of negativity of Wigner function.Numerical results show that the negativity area size and the depth of negativity of its Wigner function decrease and then v anish with dissipation. In addition,we calculate the variation of negative volume of Wigner fun ction with dissipation time.We find that it decreases with dissipation time increasing.These results s how that the nonclassical properties of the state are weakened and then disappe ar with dissipation time increasing.