The invention relates to the technical field of tanning waste source utilization and provides a method for preparing a semi-chrome tanning addition agent through waste chrome shavings and an application method of the semi-chrome tanning addition agent. Waste chrome shaving resources can be effectively converted into the semi-chrome tanning addition agent so as to be reused in the leather production and preparation processes, and the dual economic benefits of environment-friendly tanning and reduction of tanning cost are achieved. According to the method for preparing the semi-chrome tanning addition agent through the waste chrome shavings, collagen hydrolysate liquor is obtained through acid hydrolysis of the waste chrome shavings and then modified through unsaturated dicarboxylic acid andtetrakis hydroxymethyl phosphonium salt, the semi-chrome tanning addition agent is obtained, carboxyl functional groups of collagens in the semi-chrome tanning addition agent are increased, the jointpoints of proteins in the obtained semi-chrome tanning addition agent and a chrome tanning agent are increased, thus, combination and absorption of leather treated through the obtained semi-chrome tanning addition agent and the chrome tanning agent are promoted, meanwhile, the obtained semi-chrome tanning addition agent has certain tanning performance and filling property, the crust leather contraction temperature can be increased, and the fullness, elasticity and grain surface flatness of crust leather are improved.