The essential characters of dynamic feed-forward with lead-leg component are analyzed. Three conclusions are deduced: (1) when subjected to a partial ramp input, the accumulative area of output is independent of the ramp ratio, but it is only associated with the gain of the input and the lead-leg coefficients. (2) For a ramp input and a step input with the same gain, the two output accumulative areas are equal. (3) The ramp ratio only influences the peak value and the settling time of output. The dynamic feed-forward with lead-leg component has been successfully applied to the coordinated control system of #4 power unit in Da La-te power plant. Field tests reveal that the load tracking performance of #4 power unit has been improved effectively