According to characteristics of the main transmission system, spinde power and torque of riumerical control (NC)machines, the article analyzes the principle and approach of designing the stepless speed variation transmissionsystem in electromechanical series. It also tells the effect of changes in the relationship between stepped speed variation ratio and the range of steed variation on the property of speed variation. Then the programme for the power of spindle to match the property of torque is determine...