The work aims to discuss the function and value of speculative design prototypes of virtual idols in the digital era. Based on the current situation of the development of virtual idols, focusing on the development direction of the concept of speculative prototype in speculative design theory, the process of speculative prototype construction was explored and analyzed through literature research, case analysis and other methods based on fictional characters and world views with teaching practice as an example. The construction process of virtual idol speculative prototype was proposed:problem hypothesis, narrative text, fictional situation, interaction mode, and aesthetic style. As a speculative medium, virtual idols use speculative design prototypes to create fictitious theme narratives, and vividly express the speculative process of great humanistic value through the performance of characters and world views. This not only expands the design functions of virtual idols, but also helps people better understand and judge their future diversified development possibilities, providing feasible ideas for the design and development of China's virtual idol industry.