Abstract: By adopting evolution algorithm and autonomous-vision-based fitness evaluation approaches,the on-line au- tomatic gait evolution of 4-legged robot in a RoboCup soccer field is realized.We incorporate interpolation method as the crossover method,use a PC base station to conduct algorithm calculation and flow control,and adopt some time-cutting strategies.The evolutionary learning is implemented with high continuity and expansibility,and the whole learning process can be completed within 40-60 minutes.In-field gait re-learning of the ERS-7 4-legged robot is realized,and the adaptability of walking control is improved.At last,the walking speed of ERS-7 4-legged robots is increased from 27 cm/s to 43 cm/s with the proposed algorithm.