The invention discloses a unified power flow controller site-selecting method based on load variation rate index, comprising the steps of calculating grid base power flow according to grid generation, load, frame structure and operation mode data; counting load rate of each branch, and normalizing and calculating the load rates; calculating grid power flow after each branch experiences N-1 faults; counting load rate of each branch, and normalizing and calculating the load rates; calculating a line construction difficulty level coefficient for an area where a line locates; calculating a site selection adaptability index for each branch; ranking the site selection adaptability indexes of the branches, and using the front ones of the branches with maximum index value as recommended mounting branches. The site selection adaptability comprehensive index is acquired by using grid initial power flow and line N-1 mode power flow in connection with the line construction difficulty level for the area where the line locates, a recommended mounting site for UPFC is determined according to the magnitude of the index value, and the method has the advantages that the calculation is simple and calculation speed is high.