To study the impulse coupling mechanism of a pulsed laser ablation aluminum target, the direct measurement of its macroscopic impulse coupling characteristics is one of the means. However, laser ablation involves many physical processes. Therefore, analysing the impulse formation mechanism only by studying its macroscopic mechanical properties is difficult. Plasma plume ejection formed by pulsed laser ablation is an important process to induce the mechanical effect. Hence, based on studying the macroscopic mechanical properties, this paper deeply analyzes the impulse coupling mechanism of pulsed laser ablation by measuring the plasma plume and emission spectrum characteristics. In this paper, a single pulse laser with a wavelength of 1 064 nm is used to ablate aluminum targets. By constructing a fast photogrammetry system and optical emission spectroscopy measurement system, the plasma plume image, the plasma spectral image, and the plasma emission spectrum generated by laser oblique incident ablation of the aluminum target were obtained. Based on optical emission spectroscopy of the plasma plume, the Boltzmann plotting method and Stark broadening method were used to study the variation of plasma temperature and electron number density with the laser fluence at different incidence angles of a pulsed laser, respectively. Moreover, a torsion pendulum system was built to study the trend of the impulse coupling coefficient with the laser fluence along the direction of laser incident at various incident angles. The study follows the research ideas from the plume microscale evolution process to impulse macro mechanical properties analysis. The experimental results show that the luminescence intensity of the plasma plume strengthens with the laser fluence, accompanied by the rise of plume ionization degree. Moreover, the plasma temperature and electron number density increase rapidly, resulting in the impulse coupling coefficient heightening rapidly. When the laser fluence is greater than 15 J·cm-2, the plasma temperature and the electron number density are gradually saturated due to the plasma shielding effect. The change of plasma temperature and electron number density results in the decrease of impulse coupling coefficient with increased laser fluence. In addition, the plasma temperature and the electron number density decrease with the increase of incident angle, which reduces the impulse coupling coefficient. The results show that the coupling mechanism of the ablation impulse can be well analyzed using fast photography and optical emission spectroscopy. The results can provide a reference for optimising key parameters for space applications such as laser space debris removal, space micro-thruster and despinning non-cooperative targets in space.