The knowledge acquisition is a bottleneck of the artificial intelligence. How to extract knowledge effectively from the text is what knowledge engineering is concerned. Knowledge acquisition (KA) techniques give constrains to study and application of knowledge system, therefore, effective extraction of domain knowledge from text becomes the major approach to knowledge acquisition. The paper introduced the main knowledge acquisition techniques, analyzed and compared the difference of these technologies, summed up the basic steps of applying KA techniques to acquiring knowledge and finally described the latest development of knowledge acquisition techniques.