A multicrop agricultural system, including millet, wheat, rice, and soybeans, first emerged in China in the Late Longhang period and is considered to be one of the most important basic foundations underpinning the origin and development of early states in China. However, there is still a lack of studies on the specific subsistence strategies of humans from the Bronze Age, specifically addressing how widespread the multicrop agricultural system was. To explore these questions above, carbon and nitrogen isotope analysis on human bones from the Nanwa site (ca 1720–256 BC & 960–1279 AD) was undertaken to investigate the palaeodiet and subsistence strategies of the Nanwa humans. This paper also reviews the existing stable isotope data of Bronze Age humans on the Central Plains of China. The Nanwa humans from the Erlitou and Yinxu periods have a mean δ13C value of −9.4 ± 0.7‰ and −9.1 ± 0.9‰, suggesting a predominantly C4 diet, probably derived from millet agriculture or domesticated animals fed on millet. Nanwa humans of the Eastern Zhou Dynasty have a relatively low mean δ13C value of −10.5 ± 2.4‰, indicating a consumption of much more C3 foods, likely derived from rice, wheat, soybean, or animals that fed on those plants. A temporal stable isotopic comparison from the Erlitou period to the Eastern Zhou Dynasty on the Central Plains of China shows the majority of the Bronze Age humans have high mean δ13C value (−9.5 ± 1.8‰), suggesting a predominantly C4‐based diet. We infer that millet agriculture was still the primary economy for humans during the Bronze Age. However, there is a relatively large proportion of humans from the Eastern Zhou Dynasty that have decreased δ13C values, indicating a much more C3 foods consumption and diversity diet, presumably derived from a multicrop agricultural system of millet, wheat, rice, and soybean. It is possible that the trend moved from a narrowly focused, mainly millet‐based diet, to a more diverse agricultural system and was triggered by a combination of factors such as climate change, agricultural reform, social stratification, wars, migration, and so on.