In order to comprehensively and accurately evaluate reinforced-concrete-beam fire-damage state, with combination of various information from fire hazard tests and numerical simulations, MTOPSIS-GRA model for comprehensive assessment of RC-beam fire-damage state was successfully proposed. Firstly, through a series of fire high-temperature tests, vibration tests and static-load tests upon totally 10 T-shape beams, corresponding key data, such as thermodynamic-decay characteristics, was further achieved. And based on that, the above information was better compared with the results achieved by ANSYS numerical simulations and calculations. Secondly, one set of assessment-index systems for RC-beam fire-damage state, composed of post-disaster apparent characteristics, maximum surface temperature, fire duration, bearing capacity reduction, stiffness reduction and fundamental frequency reduction and other indexes, was constructed. Besides that, a comprehensive quantitative-classification standard targeting to the said assessment-index system was preliminarily determined. And by means of further optimizing assessment-index weights achieved by Analytic Hierarchy Process and Entropy-weight Method with combination forms, as well as introducing and improving Modified Technique for Order Preference by Similarity to Ideal Solution (MTOPSIS) and Grey Relational Analysis (GRA), one MTOPSIS-GRA model applicable to comprehensive assessment of RC-beam fire-damage state has been determined. Finally, by applying this way into practical post-disaster RC-beam fire-damage assessments and conducting necessary comparative analyses between the current post-disaster building-structure appraisal standard method and actual results achieved by a large number of experiments, it turns out that the assessment results achieved therein are basically consistent with the standardized assessment ones. However, the former can more comprehensively and accurately assess whole-structure fire-damage state.