The threat of cracks is very fatal for engineering structures. Usually, the main crack is fused by several secondary microcracks, so the investigation of the fusion mechanism and life of microcracks is crucial to improve the reliability of engineering structures. In this paper, firstly, the applicability and accuracy of linear elastic fracture mechanics are verified by comparing the test results and FEA results of small-scale yielding. Secondly, the fusion mechanism and life-solution of uniform and non-uniform multi-cracks are thoroughly investigated. It is also pointed out that the homogeneity of cracks is caused by the abrupt change of crack extension path by affecting the level of stress intensity factor (SIF). Finally, the effects of maximum load and stress ratio on crack fusion are explored. The results demonstrate that the maximum load has a positive effect on the ratio of the crack fusion life to the overall crack extension process life, but the effect of the stress ratio is essentially unchanged.