In order to solve the problems of low accuracy and high time consuming in the traditional photocatalytic performance analysis methods of nanocomposites, a new method for preparation and photocatalytic performance analysis of fly ash nanocomposites was proposed. Mesoporous molecular sieve was constructed, and the obtained grey massive nano TiO2/fly ash composite was inserted into the pore channels of mesoporous molecular sieve to complete the preparation of fly ash based nanocomposites. Methyl orange was used as a degradation compound to test the photocatalytic performance of the material, and the first-order kinetic model and degradation rate calculation results of methyl orange were obtained, so as to realise the photocatalytic performance analysis of the material. The experimental results show that the photocatalytic performance of the materials prepared by this method is high, and the average accuracy of photocatalytic performance analysis is 95.5%, the average time is 0.63 s.