Abstract: In the context of accelerating the low-carbon transformation of the transportation industry, prioritizing the development of public transportation is an effective strategy to relieve traffic congestion and build a resource-saving and environmentally friendly society, and the electrification of public transportation is an important part of it. To describe the clean mineral stock and its structure in megacity taxi systems, this paper takes Beijing’s urban taxis as an example, integrates the material flow analysis method and multivariate heterogeneous data to quantify the stock of eight clean minerals, including lithium, cobalt, nickel, manganese, aluminum, platinum, palladium, and rhodium, and discusses the accumulation pattern of the clean mineral stock and the end-of-life recycling potential under the scenarios of accelerated electrification and advancement of Li-ion battery cathode technology in urban taxis. The study finds that the total clean mineral stock in Beijing’s urban taxi system reaches 50 million tons from 2011 to 2022, which is a 57-fold increase in the clean mineral stock in 10 years, with lithium and manganese accounting for about 65% of the total stock. In the baseline scenario, the total stock of clean minerals is 25 000 tons; in the accelerated electrification of taxi system scenario, the total stock of clean minerals from 2023 to 2050 is only 70% of the baseline scenario; in the advancement of Li-ion battery cathode technology scenario, the total stock of clean minerals is the lowest, which is less than 50% of the baseline scenario, so it can be seen that the development of Li-ion battery cathode technology plays an important role in saving clean mineral resources. In the dual acceleration scenario of taxi system and Li-ion battery, the total stock of clean mineral materials decreases to 15 000 tons, and the lithium stock accounts for about 3/4 of the total stock, and the development of electrification and Li-ion battery technology makes the lithium supply face great challenges. This paper estimates the stock of clean mineral materials for the urban taxi system in Beijing, and the case study of Beijing is not only useful for comparison with similar cities in developed countries, but also as a reference for the sustainability transition of other types of cities.