The present disclosure relates to an apparatus and method for diagnosing a state of a battery pack, and more particularly, to an apparatus and method for diagnosing a state of a battery pack based on a SOC of a battery module included in the battery pack. According to the present disclosure, since the SOC of the battery module corresponding to an induced abnormal situation is estimated and the state of each battery module is diagnosed based on the estimated SOC, a risk factor that may occur in the battery module may be diagnosed in advance.