This paper is well targeted in researching several researches of various tool wear monitoring methods in domestic and foreign. Five important tool wear methods are deeply investigated and described in detail. Through comparing the advantages and disadvantages of each monitoring method according to practical application, and draw a conclusion that the based on multi-sensors method is considered as the main direction of the development of tool wear monitoring in the near future, which would be a great significance for improving the utilization of machine and reducing the economic losses due to the tool wear.