Until the publication of Turbidity Currents as a Cause of Graded Bedding written by Kuenen in 1950, the gravity flow theory has made a great development. However, nowadays some geologists not only argue about the turbidity theory, but also have some problems in using concept and terminology of turbidity current. According to sedimentary process of gravity flow and fluid properties, this paper raises an analytical method of gravity flow depositional system based on fluid properties conversion theory. There are several fluid processes of the formation, development and extinction of gravity flow, including multiple conversions between different fluid properties. The final conversion results determine the morphology and category of gravity flow depositional system. At the same time, the complicated fluid conversion results the sedimentary characteristics that turbidities caused by turbidity current coexist the other lithofacies caused by other currents. According to this theory, we analyze the origin and sedimentary characteristics of fan delta caused by tractivedebris flow, Nearshore subaqueous fan caused by turbidity current and slope apron caused by debris flow, and discuss the role of Fluid properties conversion theory in the identification of sedimentary systems.