In the north part of China，the power outputs of many wind farms are limited by the load following capacity（LFC）of traditional generators.This paper proposes a mixed-integer programming formulation to assess the maximum LFC of a power system.The objective of the formulation is to maximize the total spare spinning capacity of all generators in the valley load period，which is subjected to constraints including power balance，unit on/off status and generator power limits at both peak and valley load levels.Based on the formulation，a method for evaluating wind power penetration limit is also introduced considering the error of the wind power prediction and the wind power curtailment.For given installed wind capacity，the annual wind power curtailment can be simulated.By presetting the maximum proportion of wind curtailment，the allowable wind power integration capacity is acquired by a golden section search method.The proposed method has been tested on a practical power system.Simulation results show the effectiveness of the method.