Hydraulic oil contamination testing technology and several analysis methods are expounded and introduced in this paper.It is especially emphasized that the applying of automatic particle counter system, which is integrated with technologies of particle, flow, flow velocity, viscosity, temperature, laser and computer, boosts an essential improvement for the testing technology. With the new international standard ISO11171 bringing into effect, it has more significance of the standardization of hydraulic oil contamination testing and calibrating technology.