Mechanical activation of curing agent (AlPO4) was adopted to improve the adhesive strength of solar reflective coatings in this study. Mechanical activation was realized by ball milling. AlPO4 was characterized by Laser Particle Size Analyzer, X-ray Diffractometer, Scanning Electron Microscope and Zeta Potential Meter. The results showed that the particle size and crystal size of AlPO4 decreased with the increase of mechanically activated time until 40 min. Then, four typical AlPO4 were selected to prepare the corresponding solar reflective coatings. The adhesive strength and solar reflectance of the coatings were measured by Universal Material Testing Machine and UV–Vis-NIR spectrophotometer, respectively. The composition and microstructure of coatings were characterized by Fourier Transform Infrared Spectrometer and Scanning Electron Microscope-Energy Dispersive X-ray spectroscope. The results showed that the adhesive strength of coatings enhanced with the increase of mechanically activated time of AlPO4 up to 40 min, which was attributed to a higher polymerization degree and better uniformity of Si-O-Si in coatings. Besides, mechanical activation did not reduce the solar reflectance of coatings. Therefore, mechanical activation provided a feasible strategy to improve the adhesive strength of solar reflective coatings.