Abstract: The dynamics conditions of pyramid dunes(or star dunes) formation have three respects.First the flow convergent field on the non-sandy bed possess:1) over three dominant wind directions which are approximately uniform distribution,2) their intensity and frequency and sustained time in each time are different,3) their total sand transported quantity in a year is similar,and 4) monthly sand transported quantity has obvious seasonal changes.Second,none abundant sand source and the wind-sand flow with high sand transported quantity and less accumulation.Third,the dynamics action of different scale topography,and the heating power influence on desert and Gobi under-layer.On the sandy bed,the high concentration saturated wind-sand flow or oversaturated wind-sand flow often lead to the abnormal status of barchan dunes and barchan dune chains,or re-build new pyramid like sand dunes which cannot be developed into the typical pyramid dunes.

Key words: Pyramid dunes, High concentration wind-sand flow, Flow convergent field