Abstract: In view of the unstable operation problem of diaphragm filter press in catalyst preparation plant of Shenhua direct coal liquefaction project,the diaphragm filter system was modified on the basis of analysis on the diaphragm filter press system,principle and operation.Results show that the filtering slurry leaking material,filtrate leaking,pull plate deformation failure,frame,the filter cloth inspection car taking too long,are the main factors influencing the diaphragm filter press and stable operation.By using the filter press thrust plate on the takeover of compensator,increasing the closed gas water separator,leveling rail and chain wheel bearings and adopting more strong point hole in the diaphragm filter plate the press system are modified. After modification,4 filter machine faults are less,maintenance time is shortened,strengthen equipment and stable operation ability are increased,filtrate flow into the filter cake is reduced. The filter press load has been able to meet the producing load of direct coal liquefaction project requirements. Stable operation of catalyst plant basically meet the requirement of direct coal liquefaction project operation and achieved better effect.