The quality of lathe bed has a great influence on the reliability of the complete machine, and reasonable evaluation can guide the improvement of process regulation. On the basis of quantitative evaluation of the bed's quality in thermal aging process, the concept of thermal aging entropy is proposed. The cause of lathe bed quality problem are analyzed in six aspects of 5M1E. By fuzzy comprehensive evaluation, the preliminary evaluation of the six aspects is obtained, and then the entropy assessment is combined with the Vague fuzzy evaluation to attain the comprehensive weights based on the six factors. Finally the integrated weighting factors and the preliminary evaluation are used for comprehensive evaluation of lathe bed quality.