The invention provides a mechanized construction method of large underground spent fuel disposal repositories. The mechanized construction method comprises the following steps that S1, firstly, shaftconstruction is carried out; S2, outer ring construction is then carried out; S3, after the construction of an outer ring on one side of a shaft is completed, a main shield machine penetrates throughthe shaft and repeats the construction of an outer ring on the other side of the shaft in the step S2; S4, an inner ring inside the outer ring is then constructed; S5, the step S2, S3 and S4 are repeated, and the construction of the fuel disposal repositories of adjacent layers is completed; and S6, finally, an elevator is built with a hole as a supporting point. According to the mechanized construction method, multi-layer excavation of a lower space can be realized through one shaft, and the shaft is not only the starting shaft but also the receiving shaft of the shield machine, so that the construction cost is saved; and the special outer ring and inner ring circuit design of the multi-layer disposal repositories is beneficial to the shield machine to fully develop the underground spacein time-saving and efficient way, safely and environmentally friendly manners.