The spectrally selective absorbing film plays a key role in determining the collecting capability of solar thermal en-ergy in the application of solar water heater.This research experimentally investigates influences of importance pa-rameters among spray coating process on the solar absorptance,thermal emittance and collection efficiency of the selective absorbing film.Selective parameters include thickness of the selective absorbing film,median diameters of the spray,and the frequency of the coating etc.Results show that thickness of the selective absorbing film has a strong effect on the absorptance and the emittance of the selective absorbing film.The optimum collection perfor-mance of the spectrally selective films with absorptance up to 93%while the emittance down to 65%can be achieved at a film thickness of 3.3 μm.Thus,properly selection of the film thickness results in the optimum compo-sition of the absorptance and the emittance and thus the optimum collection efficiency of thermal solar energy.Re-sults also show that higher median diameters of the spray can increase the absorptance and reduce the emittance,thus has a positive effect of the collection efficiency of thermal solar energy.It is caused by redistribution of carbon particles inside spray flow,the deposition effect onto a substrate,as well as the evaporation of the solvent.