The plasma characteristics of carbon-doped glycidyl azide polymer (GAP) are investigated ablation by nanosecond laser pulses. For the GAP energetic liquid, a specific impulse of 840 s and an ablation efficiency up to 98% are obtained, which can be attributed to the low mass loss owing to the carbon doping. A comparison between the chemical energies shows that the carbon-doped GAP provides better propulsion than pure GAP. This indicates that even for an energetic liquid, an efficient approach to enhance the thrust performance is to reduce the splashing. High ablation thrust could be achieved at a low laser fluence and high carbon content.