Biomass-derived wastes as the additive of non-degradable plastics have been paid more attention due to the ever-growing environmental pollution and energy crisis. Herein, the spent coffee grounds (SCG) have been used as fillers in polypropylene (PP) after the heat treatment to realize its recycling utilization. The effect of the heat treatment atmosphere on the properties of the obtained SCG and SCG/PP composites has been investigated systematically. The results show that the residual coffee oil can be removed more thoroughly under an air atmosphere than under a nitrogen atmosphere at a relatively low cost and an eco-friendly process. The lower residual oil rate of SCG is beneficial to improve the comminution and further enhance the affinity with the PP matrix. The obtained SCG/PP composite holds lower water absorption, higher hydrophobicity, and better mechanical properties, implying its potential applications in the field of food packaging.