Rare earth and trace elements were used for the first time to analyse the source rock and source direction of Yanchang Formation of  Upper Triassic in Ordos Basin. Research shows that the sandstone and the mudstone of Yanchang Formation in central basin have same geochemical characteristics, same REE distribution mode, and same trace elements spider diagrams, it represents specificly that the light rare earth elements are enriched, the heavy ones, Eu and Ce are to the bad; The REE distribution mode is a type which inclined to the right, LREE enriched, and HREE flat; The trace elements spider diagrams shows a type of 4-peaks, 3-valleys, and 1-flat, the curve is distributed like a ladder. The geochemical characteristics, REE distribution mode, and the trace elements spider graphs of sandstone and mudstone in Yanchang Formation are identical with metamorphic rock of Archean and Proterozoic from northeast fringe of the basin, but different remarkably from igneous rock with the characteristics of heavy rare earth elements enriched, lighy elements lost, V-shape REE ditribution mode, and the spider graph of 3-peaks, 2-valleys, the curve distributed like “W”. Therefore, metamorphic rock from Archean and Proterozoic is the dominant source rock of Yanchang Epoch, and the main source is from eastnorth. In the light of source direction, depositional enviroment, sandstone petrology, geochemistry marks of rare and trace elements, delta depositional of Yanchang Formation of  Upper Triassic in Ordos basin can be divided into two systems, one is Ansai-Zhijing-Anbian delta depositional system from eastnorth, the other is Yanding delta depositional system from westnorth. On the division basis of delta depositional systems, petrology characteristics, geochemical characteristics of rare earth and trace elements of different delta depositional systems, and the evolution process of delta depositional systems of chang 6—chang 2 in Yanchang Formation have been elaborated in detail.