Abstract:The comparing analysis was done for high speed and big power working machines variable speed application with hydrodynamic and variable frequency drive. For the economics of speed control, the variable speed range should be considered, as well as load conditions requirements of working machines. When selecting speed control program, the range of speed control and corresponding load conditions, the economics of operation and maintenance and the reliability of long term work should be considered comprehensively. Gear type couplings are suitable for high speed range adjustment. Hydrodynamic planetary gear unit has the characteristics of wide variable speed range and high efficiency of speed control. In the situations of high speed and big power, hydrodynamic variable speed control is still a class of economical and reliable solution.