Hydraulic system is the control center of aircrafts. The contaminant content of hydraulic oil is involved with the serving life and failure rate of hydraulic system. How to control the oil contamination has thus become an intensive concern for improving the reliability of aircraft. In view of the three critical issues in existing researches: (i) the lack of effective methods to prevent external contaminants from the invasion; (ii) the lack of effective purification methods for liquid and gaseous contaminants; (iii) the neglect of real-time monitoring for main contaminants, this study systematically reviews the causes, risks, and removal methods of the main contaminants, especially for the gaseous contaminant. Referring to the pros and cons of available control methods, we proposed an active control method for oil contamination, an integrated control of solid, liquid, and gaseous contaminants. Consequently, we provided an active control solution in a case study of aviation hydraulic system: (i) a closed hydraulic circuit and a closed oil tank were designed to effectively control the generation rate of contaminants, (ii) a vacuum centrifuge was installed in the hydraulic maintenance circuit to efficiently remove contaminants without creating consumption costs, and (iii) the monitoring devices were installed to real-timely monitor the contaminant contents in oil. The results from the oil purification experiments and three-dimensional modeling indicate that, the active control of hydraulic oil contamination can effectively remove 98.4% solid contaminants from aviation hydraulic systems, and is able to reduce the liquid content below 50 ppm, in particular, can reduce the gas content below 2%. It is rational to see that this active method can extend the serving life and reduce the system failure rate in evidence through reducing the contaminant contents.