Abstract: The leak-before-break (LBB) analysis has been conducted on the design of nuclear pipes to exclude the hypothesis pipe rupture accident. Once a pipe system is proved to meet the LBB criteria, the auxiliary equipment such as anti-whip devices could be omitted and in-service checking work could also be reduced. Therefore, LBB analysis can decrease the complexity and improve the security of nuclear reactor design. The LBB fracture mechanics analysis includes computation of crack-opening-displacement (COD) and crack-opening-area (COA) of hypothetical crack and determination of crack stability. In the present paper, the two most commonly used engineering approximate estimation methods for LBB analysis were summarized and programmed. By the secondary development of FEM software, the numerical analysis program for circumferential through-wall cracked pipes was established to verify the two methods. After comparing the results of engineering criterion and finite element calculation, the safety margin of each method was discussed and the applicable scope of each method was determined.