Abstract: In the research of the soil erosion, the rate of slope runoff is an indispensable hydrodynamic parameter in the runoff computation and the soil erosion forecast. At present there is still no special instrument which is widely used to measure runoff rate. Based on the theories of two-phase flow, a runoff rate on-line measurement system based on LabVIEW virtual instrument platform was developed. The virtual instrument consists of the infrared photoelectric sensor, the signal processing circuit, the PCI-6040E data acquisition card as well as the correlation survey software programmed by LabVIEW. The experiment was completed in room simulation test station. The test result indicates that this measurement system is suitable for the silt content scope of 0～250 kg/m³. Taking the flow rate surveyed by the dye tracer technique as a standard value to carry out demarcating experiment, it is found that the greatest relative error of the system is 4.14%, which makes the high accuracy. Measuring slope flow velocity using virtual instrument system based on cross-correlation theory was feasible.