An in-situ evaluation method and system for loess collapsibility based on non-destructive time-domain reflection technology, includes: calculating loess dry density and mass water content; considering loess dry density, mass water content and basic physical property indicators, and evaluating loess collapsibility in situ through mathematical models. The loess collapsibility in-situ evaluation method based on the non-destructive time domain reflectometry technology of the present invention can not only realize whether the loess has collapsibility, but also has the potential to distinguish strong, medium and slight collapsibility.