Abstract: Reliability analysis models for multi-crack structure are established in this paper. These models are based on the FMPRM(Fatigue Multi-crack Propagation Random Model) and can be used to evaluate the multi-crack structural reliability. The structural reliability is the probability that the multivariate random variability controlling the crack propagation falls into a range from the equal-life curved surface(curve) to the coordinate surface(axis). It's equal to the integrity of the probability density function of the multivariate random variability in the same range. Three models are established corresponding to different conditions: CIRM(Complete Integral Reliability Model) for simple case, SSRM(Simplistic Series Reliability Model) for complex structure with small difference to each crack propagation behavior and MSSRM(Modified Simplistic Series Reliability Model) for complex structure with large difference to each crack propagation behavior. Finally, two illustrative examples are presented along with the FMPRM to illustrate the reliability.