Abstract: Red mud was used as the main raw material to prepare filling materials for coal mines. The effects of the types and amounts of activators, fly ash amounts, cement amounts, and water amounts on the compressive and flexural strength of the filling materials were studied. The research showed that activator A (mainly composed of calcium lignosulfonate and added with 0.5% of dry red mud) had the most significant excitation effect on the filling material. Under certain conditions, the compressive and flexural strength first increased and then decreased with the increase of fly ash amounts, and gradually increased with the increase of the cement amounts. The optimal strength indicators obtained through various tests were as follows, the compressive strength at 28 days was 1.30 MPa, and the flexural strength was 0.71 Mpa, meeting the relevant filling indicators. The results showed that the heavy metal elements in the red mud based filling materials met the relevant emission standards after the leaching toxicity test.