The invention discloses a low-temperature cracking and caving method of a hard roof in a coal mine goaf. The low-temperature cracking and caving method is suitable for the technical field of strengthening cracking of roofs in the coal mine roaf, and comprises the steps that a digital display thermograph, temperature sensors, a water injection pipe, a low-temperature fluid freezing pipe, a capsulehole sealer, a high-pressure water injection system and a low-temperature fluid tank car are utilized to form a plurality of cracking drill holes and an empty hole in the hard roof in the goaf sequentially; the spiral low-temperature fluid pipe, the water injection pipe and the capsule hole sealer are connected and sent into the multiple cracking drill holes, the capsule hole sealer is adopted forhigh-pressure hole sealing, cylindrical expanding sections of hole openings of the cracking drill holes are frozen to form a self-hole-sealing structure, then the multiple cracking drill holes are frozen, and the coal seam roof is cracked by water-ice phase transformation; and when the temperature sensors all rise above 3 DEG C, freezing is conducted repeatedly, and the cycle of cracking of frostheaving, melting and frost heaving is formed. The water-ice phase transformation is conducted by the low-temperature fluid to generate an expansion rate of 9.1 % to crack the coal seam hard roof, themethod is simple, operation is convenient, the cost is low, operation is easy, and the cracking effect is good.