This paper studies the internal control of subsidiaries of DLong and SSA group using grounded theory. During the process of diversification,the enterprise has established standardized internal control in various aspects and conducted internal control replication. However,compared with single enterprise,some internal control can be standardized replication in some subsidiaries,but some cannot be. Defects in the governance of affiliated and non-affiliated businesses,imbalance between centralized and decentralized governance,and inconsistent incentives and unitary assessment are the main reasons for the non-replicable internal control. The non-replicable internal control in the short term may lead to major risks in the diversified operation. By analyzing the mechanism of outstanding internal control problems in terms of authority setting,management and control mode,business process division and collaboration,ambitions of the subsidiary managers,it provides clues to open the "black box" of internal control of the enterprise groups.