“Varnish” in recent years becomes one of the most important problems that trouble the lubrication maintenance of the key dynamic equipment in petrochemical industry.By combining the different characteristics of petrochemical key machine units,the “varnish” formation mechanism was discussed,the hazards and prevention methods of varnish were analyzed.It is presented that the varnish failure of the machine unit can be effectively prevented by applying the routine varnish removal policy for the inservice oil and doing routine lubrication management.