The concept of green construction runs through the entire life cycle of buildings. The energy consumption of mechanical and electrical systems accounts for a prominent proportion of the overall energy consumption of buildings. The traditional extensive equipment operation and maintenance and pipeline layout mode is prone to cause continuous energy loss and is difficult to meet the long-term development needs of low-carbon construction. Mechanical and electrical engineering encompasses multiple systems such as HVAC, water supply and drainage, and strong and weak electricity. The operating conditions of each device are interrelated. Any oversight in the control of a single link will amplify the overall energy consumption level. This article focuses on three fundamental theories: the full-cycle energy balance of green buildings, the coordinated energy consumption regulation of mechanical and electrical systems, and the refined operation and maintenance management of building mechanical and electrical systems. It sorts out the common energy consumption control shortcomings in the current mechanical and electrical construction and operation and maintenance stages A complete set of implementation paths is established from four aspects: the design of an integrated energy-saving solution in the early stage, the optimization and layout of on-site mechanical and electrical pipelines, the intelligent time-sharing control and operation and maintenance of equipment, and the closed-loop management of energy consumption throughout the entire process. This is to reduce the ineffective energy loss of building mechanical and electrical systems and simultaneously enhance the stability of low-carbon operation of green buildings. Provide feasible technical management support for the construction and operation and maintenance of green mechanical and electrical engineering in various civil and public buildings.