Performance optimization is one of important facets for the investigation of laser thruster. Due to the limitation of hardware, effects of laser pulse waveform on lightcraft performance have not been carried out widely in the field of laser propulsion. Based on actual pulse waveform of two CO2 lasers, two groups of energy injecting models are formed, whose temporal waveforms are similar, single pulse energies are the same, but peak powers and pulse durations are different. Performances of parabolic laser thruster obtained by numerical calculations are compared under the conditions of different pulse waveforms. The results indicate that peak power and pulse duration are important parameters in determining the lightcraft performance and waveform with shorter duration and higher peak power is more efficient in improving impulse coupling coefficient and force. The numerical results of impulse coupling coefficient with two actual pulse waveforms are 40.9×10-5 N·s/J and 30.0×10-5 N·s/J respectively, which are consistent with experimental ones reported by other literatures. The presented method and investigative idea can be used in pulse waveform design of CO2 laser and provide some reference for laser propulsion research.