Abstract: The cut-and-fill mining is one of the main parts commonly used in green-coal-mining system. No matter what kind of filling，the gob stowing cannot achieve an ideal effect in practice. The filling effect is random in certain scope. With the aid of stochastic finite element method，three situations of gob stowing consisting of full mining of coal seam with full backfilling，full mining with partly backfilling，and partly mining with partly backfilling，were analyzed. Through a lot of random calculation，it is shown that the surface settlement and deformation of the gob roof is more sensitive to filling effect. The most disadvantageous factors should be taken into consideration to guarantee that the filling effect should meet the design requirements as far as possible. The degree and range of variation in filling effect should be strictly controlled to ensure the filling to achieve the expected goal.

Key words: Goaf, Stowing effect, Stochastic calculation