Abstract: To achieve an efficient and safe operation in Underhand drift stoping，the mechanical model of thin plate with downward drift was built by using elasticity mechanics and a criterion for tensile strength failure of filling body was obtained.Then the economic model of downward drift stoping P(h/M) was built.In the case of a gold mine in Shandong，the relationship between height and width of different drifts and economical index of downward drift filling was analyzed when safety coefficient is 1.8.Research shows that the relationship between economical index and drift width is in linear growth，while the relationship between economical index and drift height is a negative power function.When M≤1.5 m，economical index drops significantly.While economical index falls slowly as M>1.5 m.Therefore，the economical index is analyzed when a half width of drift ranges between 1.3 m and 1.7 m，and height ranges between 2.8 m and 3.6 m.It is recommended that the analysis results of safety factor，l=1.5 m，M=3.6 m，h=1.49 m，should be substituted by analysis results of economical indexes l=1.4 m，M=3.6 m，h=1.40 m，for the filling cost has decreased by 1.64 yuan per cubic meter.Therefore，this research has great theoretic value and realism significance.

Key words: Thin plate model, Downward drift, Safety coefficient, Economic index