Abstract: ‍ ‍A heterogeneous cell-free multiple-input multiple-output （MIMO） system is one of the development directions of future mobile networks， as it is an efficient communication system with great energy saving potential. This paper first introduces the overall architecture of heterogeneous cell-free MIMO systems； then analyzes the specific architecture and energy saving potential of the network from a holistic perspective； and introduces the basic principles and potential energy saving gains from green network deployment and collaboration， network operation and scheduling， user access， energy-efficient MIMO transceiver technology， and transmission and multiple access. With the development of information metamaterials， several novel heterogeneous MIMO transceivers have gradually shown their advantages in energy efficiency. Rational use of these new transceiver technologies will effectively improve the energy efficiency of the system. In addition to the gain brought by the hardware， the gain of heterogeneous cell-free networking mainly comes from the massive MIMO formed by the cooperative transmission of various access points， which also brings more complex signal transmission modes. Simultaneously， limited by computing resources， the system cannot cooperate in an unlimited manner； thus， research must be conducted on the deployment strategy and cooperation mode of the access point of the system. After deployment， in response to large changes in the user’s communication needs in space and time， deep learning and other technologies can be used to predict the user’s behavior to a certain extent， and adjust the operating state of the communication equipment in space and time， to meet the communication indicators and improve the energy efficiency of the system. Finally， the user’s multiple access and transmission mode is the basis of the entire heterogeneous cell-free MIMO system， and the new rate-splitting multiple access （RSMA） technology can effectively combat interference. Transmission beamforming for heterogeneous cell-free MIMO systems also requires a new design to adapt to RSMA technology and heterogeneous MIMO devices. This paper also discusses the possible design and future research direction of the abovementioned aspects.