Since the problems of significant rock clamping effect and ore depletion were caused by deep hole blasting in steeply inclined thin veins, a combination of on-site investigation, PMMA (organic glass) blasting model experiment and numerical simulation was used to explore the mechanism and a quantitative characterization method of rock clamping effect by taking a gold mine in Gansu Province as the engineering background. Firstly, to analyze the distribution pattern of blasting cracks under different mining conditions of thin ore veins, a PMMA blasting model experiment was conducted. The results show that reducing the mining width of the thin ore veins reduces the radius of blasting crushing and fracture areas around the blast hole and suppresses the development of blasting cracks. Furthermore, different blasting conditions of thin ore vein mining were simulated. The results show that as the mining width of thin ore veins decreases, the blasting energy reflected and superimposed at the blasting-free surface decreases, and the volume of blasting rock decreases accordingly. Meanwhile, more blasting energy is dissipated as kinetic energy, which could not be effectively used to break the rock. Finally, a quantitative characterization method for the clamping coefficient of thin ore vein blasting was proposed based on the analysis of blasting energy. A clamping coefficient was defined by the ratio of the total energy peak at the center point of the blasting free surface under semi-infinite and narrow amplitude working conditions, and this index characterized the size of the clamping effect. As a result, a prediction model for the blasting clamping coefficient was established through the mining width and rock mechanics parameters. The study of this paper can provide a theoretical basis and technical support for the optimization design of deep hole blasting parameters in steeply inclined thin ore veins.