Local scour of a pile foundation in offshore wind farm is one of the important parameters in engineering design and operational stage. Based on the local scour data measured in-situ 3 times at a pile foundation in an offshore wind farm in Zhanjiang, the maximum depth and radius of scour pits and the changing characteristics of scouring and silting are analyzed and studied. The maximum depth and radius of the scouring are calculated according to the empirical formula of local scour of pile foundation and by using marine hydrodynamic data measured in the engineering sea area, and then the calculated values are compared and analyzed. The results indicate that under the protection of scour-proofing facilities, the maximum scour depth of the pile foundation measured in-situ 3 times is stabilized basically at 4.0 m and the ratio of maximum scour depth to pile diameter is 0.57. The ratio of the maximum scour depth to the pile diameter calculated by using the empirical formula is greater than 1.1, indicating that the scour-proofing facilities for the pile foundation have a certain effect. The values calculated for the scour pit radius are in good agreement with those measured in-situ. It is therefore suggested that during the operational stage of an offshore wind farm the monitoring and protection of the scour pits of the pile foundation should be enhanced further.