Nowadays, the determining of the coefficient of friction is of great significance to the policy of energy and material saving. Due to the limitations and ambiquity of the old frictional law, this paper points out the necessity of analysing the physical interpretation of coefficient of friction. From the data of coefficient of friction and its variable law obtained through a series of tests made on metal, a supplement to the physical interpretation of the friction coefficient is suggested. It is also considered practical to Set up a measuring standard and data bank for determining the friction coefficient instead of finding a unified mathematical model as it is only through testing and measuring could the friction coefficient be obtained.