Abstract: In order to improve the flowability of the manufactured sand and unclassified tailings coarse aggregate paste slurry, two types of water reducers, polycarboxylate superplasticizer （PCS） and naphthalene series superplasticizer （SNF） are used to study the effects of different water reducers and their additive amounts on the yield stress, viscosity, spread and strength of the filling slurry. The results show that both types of water reducers can improve the flowability of the filling slurry, and the naphthalene series superplasticizer water reducer has a significant improvement effect on the flowability of the filling slurry. Compared with the filling slurry without the addition of water reducer, when the addition amount of naphthalene series superplasticizer water reducer is 1%, 2%, and 3%, the yield stress is reduced by 50.30%, 84.08%, and 100%, respectively, and the spread is increased by 75%, 131%, and 234%. Under a certain filling ratio, adding two types of water reducers can reduce the early age strength of the filling body, but when the amount of water reducer added is 1%, it can improve the late age strength of the filling body to a certain extent.