Based on the veracity，cost，and reliability problems of the on-line monitoring device for the transmission line safety evaluation，a novel method of the line ontology structure safety evaluation is proposed，which works by checking the operating stress of the components and their actual strength.By applying reductionism and inversion theories，a multimode line mechanical model is developed under complex conditions，and the calculating formula of the stress for the corresponding components is derived.By taking the influencing factors of long-term operation and the uncertainty of the experts' knowledge of the evaluations into consideration，a fuzzy comprehensive evaluation model is built.On the basis of the J2EE struts-spring-hibernate（SSH）three-tier architecture，the corresponding software system is designed and realized.Examples are given to prove the validity and reliability of the system.The results provide the scientific decision basis to the power-grid for safety measures and pre-control.