The present disclosure relates to an ISG control system and an ISG control method for a construction machine capable of controlling ISG even in a working state of a construction machine, the ISG control system including: a surrounding environment determinator configured to determine surrounding environment of the construction machine; and a vehicle controller configured to determine whether the construction machine is in a working state or a traveling state based on a determination result from the surrounding environment determinator, wherein the vehicle controller controls an engine based on a preset work ISG condition when it is determined that the construction machine is in the working state, and wherein the vehicle controller controls the engine based on a preset travel ISG condition when it is determined that the construction machine is in the traveling state.