The inversion method of temperature and pressure from the upper and middle troposphere to the lower stratosphere is studied and simulated. An absorption line is selected， which is not sensitive to temperature but sensitive to pressure， and the relationship among the absorption cross section， pressure and the absorption coefficient is used to determine the pressure by using the iterative method. An absorption line is selected near the weak absorption peak and the relationship among the absorption coefficient， pressure and temperature is used according to the retrieved pressure value to determine the temperature by using the iterative method. In order to reduce the influence of other absorption and scattering factors on the inversion results， the simulation process adopts the method of differential wavelength. In the oxygen absorption band， the appropriate absorption line is selected， and the profile of the differential absorption coefficient at the tangent altitude of each laser track is obtained by retrieving the simulated data of the laser occultation differential transmittance from the Abel integral inverse transformation， and then the pressure and temperature at each tangent altitude are retrieved using the differential absorption coefficient. The simulation results show that the inversion error of pressure is primarily affected by the inversion error of the differential absorption coefficient， which increases with altitude decreasing， and the maximum error is approximately 6%； the inversion error of temperature is affected at the same time by the inversion error of pressure and the differential absorption coefficient； the two influences are partially offset， and the maximum error is 1.5 K near an altitude of 5 km. Through analysis of the error model， some change trends and influence factors in the inversion error are explained. Under the condition of eliminating the inversion error of the differential absorption coefficient， the pressure and temperature are solved once in a cycle， the maximum inversion error of pressure is approximately 0.3%， and the temperature is approximately 1 K. The comparison between this inversion error and the inversion error of the differential absorption coefficient highlights the importance of reducing the latter.