Weed identification technology is the key to the realization of selectively spraying herbicide for the environmental protection. In order to promote the research and application of this technology in China, the research methods and advances of weed identification technology using machine vision in precision farming were analyzed. The theory, feature parameters, research advances and problems using the shape, texture, color and multi-spectral features to identify weed were discussed, respectively. The difficulties of real-time identification were concluded.