Abstract: Because of the inaccuracy of laboratory test results of self-weight collapsibility of deep collapsible loess and the lack of in-situ test methods for testing loess foundation collapsibility, a new field test method, the sand-well load immersion test method, is proposed based on the existing sand-well immersion test. The core is that after the loess under the sand well has settled stably under the action of test pressure, the collapsible loess under the bottom of the sand well and around the sand well can be quickly saturated due to the strong permeability of sand and gravel in the well, therefore the collapsibility of the loess under the bottom of the sand well and the self-weight collapsibility of the loess around the sand well can be measured. Through two sets of sand-well load immersion tests, the collapsible deformation of different depth strata under different pressure and immersion conditions is tested, and the sand-well load immersion test and the large test pit immersion test adjacent to the site are compared and analyzed. The results show that the judgment results of the sand-well load immersion test are consistent with the test pit immersion test, indicating that the sand-well load immersion test is feasible. In addition, the sand-well load immersion test has the advantages of short cycle, low cost, low site condition requirements, small water consumption, etc. The sand-well load immersion test is suitable for the study of collapsibility of deep loess. The results are of a certain reference significance for the collapsibility evaluation of loess engineering in the loess area (especially deep loess).