A six-temperature multifrequency dynamical model of pulsed CO2 lasers is presented, taking account of the collision-dependent overlap of rotational lines, the effect of hot bands and sequence bands on the gain spectrum, and non-Lorentzian line overlap effect in a wide range of pressures from 20 torr to 20 atm. Theoretical calculations of pulse shape and laser spectrum have good agreement with experimental results. This model should be useful in the understanding of pulsed CO2 laser dynamics, in the evaluation of alternative pump schemes, and in the investigation of tunable characteristics. Thus it can provide theoretical support for the design of pulsed CO2 lasers.