[Objective] Exploring the topsoil grain size distribution and its sedimentary environment, to provide theoretical bases for ecological restoration and effective sand disasters control in the Dunhuang desert-oasis transitional zone.[Methods] Surface sediments were sampled by diagonal method in Dunhuang desert-oasis transitional zone, Grain size parameters were calculated by moment method. The spatial distribution and sedimentary environment of grain size were analyzed.[Results] (1) The contents of extremely coarse sand and extremely fine sand were both low in the research area. Desert and oasis were mainly composed of coarse sand and fine sand, and the transition zone was dominated by mid-sand. The grain size decreased from desert to oasis. (2) The sorting of the 3 sampling belt transects performed all better, among which, the desert was the best, followed by the transition zone, the oasis was the worst. (3) As for skewness, desert and transition zone were nearly symmetrical distribution, while oasis belonged to positive skewness. Kurtosis type was plat, which showed that responses of different sediment grain sizes to wind power were different.[Conclusion] The sand of oasis is dominated by aeolian environment, Mingsha mountain is mainly lacustrine or river environment, two different sedimentary sands appeared in the transitional zone.