Abstract: Backfill strength in deep mining is commonly determined by analogy with shallow mining experience at present. In order to change this unreasonable situation， non-linear constitutive models of crude tailing backfills (CTBs) before peak strength were constructed based on uniaxial compression experimental results of CTBs in a deep mine， and the equation of necessary compressive strength was consequently derived based on the principle that there is approximate energy loss within a backfill and surrounding rock compound system. It is proved by a case study that the non-linear constitutive model of CTB before peak strength is identical to the experimental result and that the CTB strength in deep mining is related not only to the mechanical performance of the CTB itself， but also to the in-situ stress and elastic modulus of surrounding rock. The case study also suggests that the calculated necessary backfill strength by the non-linear constitutive model is more accurate than that by the linear constitutive model.

Key words: crude tailings, constitutive model, deep mining, strength of backfill