This paper discuss the numerical simulation of impeller rotational speed's impact to force flow trace experiment. Final tracer concentration duration curves indicate that the in the flow field of karst caves, the time inflection points appear on tracer concentration duration curve are brought forward as the hydrodynamic condition is promoted, and in 1D karst caves, tracer concentrate correspond to inflection points reduce along with the ascension of the hydrodynamic condition, in 2,3D karst caves, it may rise the phenomenon that tracer concentrate correspond to inflection points rise along with the ascension of the hydrodynamic. In 2,3D karst carves, when hydrodynamic intensity is small, the tracer's migration has little to do with the hydrodynamic conditions and increase steadily as the hydrodynamic conditions promote, when hydrodynamic intensity is large, tracer migration rate rise in nonlinear as the hydrodynamic conditions promote. Therefore, through the analysis of the force flow tracer curve's shape can roughly deduce the underground karst cave's spatial dimension.