In urban China, urban resident annual earnings are 1.3 times larger than long term rural migrant earnings as observed in a nationally representative sample in 2002. Using microsimulation, we decompose this difference into four sources, with particular attention to path dependence and statistical distribution of the estimated effects: (1) different allocation to sectors that pay different wages (sectoral effect); (2) hourly wage disparities across the two populations within sectors (wage effect); (3) different working times within sectors (hours effect); (4) different population structures (population effect). Although sector allocation is extremely contrasted, with very few migrants in the public sector and very few urban residents working ...