This paper reported a novel method to measure photoinduced acid generation in polymer films, which were widely used in microlithography. The method employed Rhodamine B (RB) as acid sensor due to its changes in color and uv-vis absorbency in acidic condition. The property of Rhodamine B was examined in hydrochloric and trifluoromethyl sulfonic acids, and the standard working curves in thin polymer film were set up, which indicated the relationship of acid concentration and Rhodamine B’s relative peak absorption ("ABS). In this case, the difference in absorbency could reflect the different amounts of acid generated. According to these standard working curves, we can calculate the efficiency of photoacid generator (PAG). This method has advantage over existing method in measuring the efficiency of photoacid generator in solution, because it eliminated the influence of solvents.