The article mainly introduces the research progress and development prospects of low dimensional, low-density multi-principal element alloys. Multi-principal element alloys typically include medium entropy alloys and high entropy alloys. High entropy alloys overcome the limitations of traditional alloy materials in strength and toughness through the design concept of “entropy regulation”, exhibiting excellent mechanical properties. However, the drawbacks of high density and cost limit its widespread application. To address these issues, researchers have developed low dimensional medium and high entropy alloy materials and low-density high entropy alloys (i.e. light-weight high entropy alloys). The article provides a detailed introduction to the preparation methods, performance characteristics, and development prospects of low dimensional medium and high entropy alloys, as well as low-density high entropy alloys. One dimensional multi-principal element alloys, namely medium and high entropy alloy fibers, are mainly prepared by hot drawing, cold drawing, and glass coating methods. They exhibit excellent mechanical properties at both room temperature and low temperature conditions, and have broad application prospects in fields such as high entropy alloy fiber flexible materials and composite materials. Two dimensional high entropy alloys, also known as high entropy films, can be prepared through techniques such as physical vapor deposition, exhibiting ultra-high hardness and good high temperature stability. They have enormous potential for applications in extreme conditions such as aerospace and energy. Low-density high entropy alloys, also known as lightweight high entropy alloys, not only have the characteristics of high strength, corrosion resistance, and high temperature resistance of high entropy alloys, but also have the advantage of low density. They will play an important role in extreme environmental fields such as aerospace.