In order to develop a technology that can quickly monitor the aging state of heat-resistant steel, it is necessary to ensure the safe operation of the equipment. Laser-induced breakdown spectroscopy (LIBS) was applied to the rapid evaluation of the ageing state of heat-resistant steel, and a new method for ageing grade evaluation based on LIBS photoacoustic multimodal information fusion was proposed. The recursive feature elimination method was used to screen the features of the LIBS data, and the acquired acoustic wave time-domain signals were converted into spectral data by time-frequency analysis, and the acoustic characteristics reflecting the changes of the mechanical properties of the materials were obtained. The effects of two multi-source information coupling strategies of "dimensionality reduction first and then fusion" and "fusion first and then dimensionality reduction" were systematically compared, and the ageing level evaluation model was constructed by linear discriminant analysis and support vector machine. The results show that the proposed photoacoustic multimodal information fusion method significantly improves the accuracy of ageing assessment, and the model accuracy is 97%, which provides a new technical path for the rapid monitoring of the service status of heat-resistant steel.