Abstract: This paper focuses on the size effect for compress strength of cemented tailings backfill,which obtained by uniaxial compression test with packing specimens in different shape or size,aiming to explore the size effect for compress strength of cemented tailings backfill phenomenon and the strength conversion among the backfill with different shape or size.The test results show that the compress strength of a bigger size filling body is higher than that of a smaller one;The relationship of uniaxial compress strength among is a power function,the strength conversion of backfill between different shape or size can be expressed by a same function which is independent with tailing-cements ratio and slurry concentration.