The strength of the backfill body is the key factor to ensure the stability of goafs,so it is necessary to calculate the strength of the backfill body.2 theoretical calculation methods,the Terzaghi model method and the Lupin calculation method,are used to calculate the backfill body strength in Tiaoshuihe Phosphate Mine.To ensure the safety of the mine,the safety factor is taken as 2.0 and the result is 0.76-1.84 MPa.To ensure its accuracy,Flac3D numerical simulation software is used for strength verification and the result is 1.5 MPa,which is within the range of theoretical calculation.The 2 calculation methods are consistent,showing that the calculation of the strength requirement is reasonable.