Abstract: Once water-conducting cracks induced by coal mining contact an overlaying water body, water will flow and burst into mine, directly threating safe production in coal mine. The paper, on the basis of analysis and summing up of existing research methods of water-conducting, from theoretical derivation and in combination with production practices, analyzed the relationship between the height of water-conducting crack and the mining thickness and stratum properties, found the clear proportional relation between the height of water-conducting crack and the square root of mining thickness. It was pointed out that the relationship between limit coverture increment and stratum properties and mining thickness plays an important role in determination of the height of water-conducting crack when mining is conducted below bedrock with clay alluvial soil or similar rocks. The bedrock with clay alluvial is impossible to penetrate by descending crack when its thickness is more than double mining thickness. The paper provides a basis for future research on crack in specific coal mining conditions.