Abstract: In situ dynamic study on friction and wear behavior in a scanning electron microscope (SEM) is one of dynamic microscopic research ways developing in 70's this century,which can be used to trace the processes both in debris forming and wear tracks developing and to know the true facts of behavior of materials surface under friction and wear as well.A newly developed wear test rig installed in a China made SEM has already been adopted to do some wear experiments on a friction pair of steel 15 # steel 45 #.The results have come out and show that there always is a stick slip phenomenon inthe whole process of sliding between steel 15 # and steel 45 #,and the micro cutting is the main mechanism of sliding wear.At this experiment conditions the developing of wear track shapes can be distinguished into five stages:(1)The transverse veins being vertical to the sliding direction are appear,(2) Big flake like debris stripping are brought about,(3) There are the flake like debris stripping caused by fatigue,(4)Big block debris and big pits on surface are produced,(5)The wear tracks tend to become flat.The major advantage of using such device to study friction and wear is that either dynamic or quasi dydamic observation can be done.These two kinds of observations are equally important to dynamic study on friction and wear process.