Abstract: A nanosecond pulsed laser was used to study the impulse coupling characteristics of typical metal materials with millimeter ablation spot size. The impulse characteristics of laser ablation were studied based on a typical torsion pendulum measuring system. By using the method of translational fitting of the local least square method, the experimental data of small-displacement generated by torsion pendulum vibration were preprocessed, and the interference of noise to impulse measurement was avoided. A measurement method of millimeter scale ablation spot size was designed. On this basis, the impulse of millimeter scale spot irradiating metal target Al 5A06, TC4, 30CrMnSiA was obtained in the experiment. The results showed that the impulse generated by irradiating titanium alloy TC₄ was the largest at the same laser fluence. And the maximum impulse coupling coefficient generated by irradiating TC₄ was greater than that of Al 5A06 and 30CrMnSiA. However, the optimal laser fluence of TC₄ was the smallest among the three materials. In order to analyze the influence of the ablation plume on the impulse coupling characteristics, the plume transmittance at different laser fluences was estimated. The results indicated that a large amount of incident laser energy was absorbed by the ablation plume when the plume transmittance was lower than 0.3, which caused a decrease of the impulse coupling coefficient.