Abstract: The finding of failure mechanism in a frame structure and the reliability analysis is mainly discussed. The finding of failure mechanism is done step by step with linear elastic-plastic analysis which is based on the analysis of elastic matrix. The relation between the failure mechanism form and the load can be found after the following processings: a correcting the simplified structural draw of plastic hinge; b. treating the plastic resistant moment. The Availability is calculated with the conditional probability considering the effect of plastic moment redistribution.