To describe the real flow field of the Hongze Lake under different hydrologic and weather condition, GPS tracers were installed at the main entrances of the lake to visualize the real time tracking of water surface trajectory and flow direction, and the preliminary flow field map of the Hongze Lake was formed. The field tracer experiments show that the water flow path in the center of the lake is a curve from west to east. When the inflow is small, it is difficult for water to enter the central flow field of the lake. When the inflow is large, the spatial distribution of flow velocity is uneven and the flow field is complex. It is also found that the water flow is affected by the surface wind field of the lake under the condition of small flow rate, whereas the main influencing factor of water flow is its own flow field when the flow rate is large. At the same time, a two dimensional hydrodynamic model was built to simulate the flow field of Hongze Lake under different inflow conditions. The simulation result shows that the simulated flow field is basically consistent with the result of the GPS tracer experiment. GPS based tracking experiment method is applicable to the analysis of the spatial variation of hydrodynamic forces in rivers and lakes, it can also provide some insights for the transport and diffusion of sediment and pollutants.