Article dans une revue: 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 (working time effect); and (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 as self-employed, this has no clear impact on earnings differentials, because the sectoral effect is not robust to the path followed for the decomposition. The second main finding is that the population effect is robust and significantly more important than wage or working time effects. This implies that the main source of disparity between the two populations is pre-market (education opportunities) rather than on-market.