Ablation heat can be not only used to represent the capability in laser-hardening of composite, but also to describe the laser processing efficiency. Experiments are conducted to analyze the influence law of tangential airflows velocity at low subsonic and laser intensity on laser ablation heat of glass fiber reinforced epoxy resin composites. It shows that laser ablation heat decreases rapidly with the incident laser intensity firstly and then become stable at the same airflow velocity, when the laser irradiance is in the range of 100~500 W/cm2. The pivotal point of the ablation heat is about 200 W/cm2. On the condition that the laser intensity is below about 200 W/cm2, laser ablation increases with the airflow velocity with the same laser irradiation. On the contrary, laser ablation decreases with the airflow velocity. Ablation mechanism analysis indicates that the variation of utilizing efficiency of incident laser energy is attribute to the competition of multiple factors which include thermal diffusivity in material, surface combustion of pyrolysis gas, oxidative ablation of pyrolytic charcoal, radiation induced energy loss, and airflow denudation effect.