In order to solve the problem of coal mining under villages, high concentration cemented backfill mining is employed in Xinyang Mine. Fly ash is the important factor that affects high concentration cemented backfill material’s performance. To determine the reasonable proportion of fly ash in backfill material, the material’s mechanical and transmission performance was analysed with the dosage of 18%, 20%, 22% and 24%. The results showed that the strength of the backfill body increases with the dosage’s increase, but the growth is not obvious; the frictional resistance also increases, and the local resistance decreases first and then increases, and the dosage of fly ash has greater influence on frictional resistance than local resistance; the reasonable proportion of fly ash that meets the backfill material’s mechanical and transmission performance is 20%.