The output properties of a hybrid configuration containing a low pressure and an atmospheric pressure pulsed CO2 laser are theoretically analyzed. The simulation is performed based on the Six-Temperature Vibrational-Rotational Dynamic Model (6TVRM). The laser discharge tube is modeled by a non-linear distributed lumped electric circuit and the electron density is calculated by Transmission Line Method (TLM). The rotational transitions affecting the population of the upper and lower laser levels are also taken into account. The calculations were done by solving a set of differential equations using Runge-Kutta method in MATLAB software environment. It has been shown that using the above mentioned models leads to a significantly better agreement of the simulation results with the associated experimental data.