Abstract: Investigates the useful application of towing torque. Lubrication oil flux is supposed to be controlled. Both theoretical analysis and experiments proved that the towing torque increases with the increases of lubricating oil flux. If the lubricating oil flux is controlled from minimum to its maximum value, a linear increase in load torque can be obtained. That means lower load could be utilized in hydroviscous dynamometer and the scope of its load testing power could be enlarged. Furthermore, the minimum clearance between friction plates satisfying the minimum power loss is given.