In the frame of the unified expansion theory(UET) we obtain the higherprecision expressions of the UET by means of improving the accuracy of calculation,andthen extend it to the laser systems.Two single-mode dye-laser models are studied by themodified UET, and the expressions of stationary probabilities, means and variances laserintensity are obtained. Comparison shows that the results of the modified UET agree wellwith the exact numerical results and the simulation results better than the results of the unified colored-noise appreximation (UCNA).