We have a cylinder used for granulation,this cylinder is driven by motor 90 Kw via a gearbox,
there is a mechanical problem that result in a fluctuation in motor current from 70 A to 130A ,
i ask if this fluctuation has a negative effect on motor.

You should compare the motor current with the nominal current stated on the motor nameplate. Assuming that the motor is designed for 400V, it does not seem to be excessively loaded, so provided the current fluctuations is not accompanied with excessive vibrations, it may not be a big problem in itself. If you over time experience undue wear of the motor, you can replace it with a heavy-duty version eventually.

If the name plate of the motor nominal current is exceeded then I replied Yes. First step for more details can be measured without load, and then compare it with the use of load. Regards.

As long as the phase current is balanced and the 130A is less than or equal to the rating of the motor, you should have nothing to worry about.

your motor winding insulation may deteriorate slowly, if you exceed much from the nameplate current ratings... you must address the root cause of the motor current fluctuation since the amplitude of current rise may be worsen as the motor service run progresses...