What's wrong about of blower of mill

I have a mill. It is always vibraitng. Who can tell me why and how to solve? Thanks

Causes:Too much powder on vanes, vanes worn out, and fastening-bolts loosened.
How to Fix:Get rid of powder on the vanes, to fix the bolts

If there is a rotating mill and / or a rotating blower, there could be vibration of both or either from the same types of causes. I will address the blower. If the drive connection to the motor is with a flexible coulping is the shaft alignment proper ? Are the support bolts tight on the blower and the motor ? Are the fan housing assembly bolts tight ? Is it rotating in the proper direction ? Is the shaft bent ? Is the fan rotor dirty or are there broken blades ? Are the V-belt drive sheaves warped or broken ? Are the drive belts loose or deffective ?
Are the fan and motor bearings tight, lubricated and without defect ? Is there a 90deg elbow close to the blower inlet or is the inlet connected to a straight piece of duct ? How about the outlet ? If there are inlet guide vanes in the blower, are they oriented properly ? If this is a high speed blower is it operating close it the cirtical (resonant) speed ?
Is the blower operating at reduced capacity so that it is operating in the unstable region of its performance range ? If the fan and motor are on a unitary support, could it be flexing ? If there are vibration isolation springs or pads, are they deffective ? How is the flexible connection in the inlet and/or outlet ?

You really haven't given enough information. You could have a problem in a bearing set or you could have a structural mode being excited by one of the harmonics of the blower. Also, you could have a vibration isolation system that is incorrectly sized, has failed, or one needs to be installed.