Additive manufacturing (AM) has significant advantages over conventional manufacturing technologies, including freedom of design, mass customization, and the ability to produce complex structures. Because reducing manufacturing energy is an essential challenge for industrial sustainability and national economics, the trend toward AM motivates us to explore the energy consumption of AM to address energy efficiency. Existing energy consumption quantitation methods for AM parts require complex models, and the energy consumption characteristics of AM equipment muse be considered in the quantitative analysis process. Therefore, a feature-based energy consumption quantitation method for complex AM parts is proposed that uses a simple model and can be applied to different AM technologies. A feature segmentation method is first proposed to divide complex AM parts into typical AM features (AMFs). Then, the energy consumption model is developed for each AMF to quantify the energy consumption during fabrication of the entire part. Finally, the energy consumption characteristics of a typical mechanical part manufactured by three different kinds of AM processes—fuse deposition modeling (FDM), stereolithography (SLA), and selective laser melting (SLM)—are investigated using the proposed feature-based energy consumption quantitation method and measured in an experimental case study. The results show that the proposed method can effectively and quickly predict the energy consumption of AM part manufacturing. Moreover, the efficiency of different types of AM processes is compared and discussed to address applicable efficiency improvement methods. This method can predict the energy consumption of complex AM parts, and can be integrated into the AM three-dimensional software model, providing a reference for structural optimization of AM parts.