Abstract: Strengthening the Party by theory is an important part of Xi Jinping's Thought on Party building. It is a theoretical innovation in Party building. It is an action guide and fundamental compliance for comprehensively and strictly governing the Party in the new era. Xi Jinping's important exposition on strengthening the Party by theory is the innovation and development of Party building theories in the new era， and it clarifies the direction， mission and basic requirements for Party building in the new era. The foundation of strengthening the Party by theory is theoretical innovation， its essence is theoretical armament， its purpose is theoretical practice， and its pursuit is theoretical confidence. The scientific promotion of theoretical thinking， the spiritual pursuit of ideals and beliefs， the value pursuit of essence realization， and the objective requirements of changes in the times are the driving forces for strengthening the Party by theory. The coordination of system and governance should be strengthened and actively promoted from the four dimensions of strengthening overall planning， learning and understanding， unity of knowledge and belief， and transformation of subject and object.

Key words: Communist Party of China; strengthening the Party by theory; theoretical innovation; theoretical armament