During the deployment of 5G it has become apparent that 5G base stations consume excessive amounts of energy. However, there has been little investigation or discussion of this issue in theoretical research circles. This article examines this problem by comparing 4G and 5G from three perspectives: theoretical analysis of communication systems; their high-order modulation constellations and carrier aggregation; and their base station downlink schemes in industrial standard. The basic conclusion is that the mobile communication system with multiple modulation technologies is designed theoretically by considering energy efficiency and spectral efficiency, but the actual energy consumption exceeds the operator’s expectation. On the basis of this, possible future directions for improving spectrum efficiency and reducing energy consumption are proposed.