Vacuum preloading technique was used to deal with the dredged sludge and the jet vacuum device was adopted. The adjustable vacuum degree device has the advantage for the dredged sludge treatment process. By using the test rig of jet pump, the vacuum adjustable ways and methods were experimentally studied. The results are as follow: when changing the parameter m, which represent the area ratio of throat and nozzle, different gas suction ability and vacuum degree will be obtained. According to vacuum preloading technique construction stage, nozzles with different diameter can be replaced in jet pump to meet different needs. Distance between nozzle outlet and throat inlet L has an optimized value, during the process of adjusting the distance L toward the optimal value, the vacuum degree in jet pump was changed, but the changing range was limited. There is a small influence on the adjustable vacuum degree when changing the length of throat. The highest vacuum value can be achieved with a vertical installation of the jet pump and with long length of throat. The vacuum value appears a logarithmic growth with the nozzle jet intensity, thus changing the working pressure in front of nozzle is a suitable way for vacuum adjustable. There is a good prospect in other applications when the vacuum degree can be adjusted accurately.

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