The present invention relates to a system and method for diagnosing cracking in a solidified shell in a mold, in which whether longitudinal cracking has occurred in the solidified shell can be diagnosed in real time by using a variation in temperature of the solidified shell in the mold during a continuous casting process. The system comprises: a plurality of temperature sensors arranged in a matrix form in a mold, wherein the plurality of temperature sensors are divided into a first group and a second group based on where cracking occurs; and a processor configured to: calculate a temperature difference between the temperature of the first group and the temperature of the second group from the temperatures detected by the plurality of temperature sensors; and determine, using the calculated temperature difference, whether cracking has occurred in a solidified shell discharged from the mold.