The morphological comparison researches on Eriochair japonica and E.sinensis in different water systems of the Liaohe,Yantze,Oujiand,Minjiang and Nanliujiang River were reported.The major morphological difference of the mitten crabs(E.japonica and E.sinensis) are subsquare or second circular in carapace;obtuse or sharp in frontal teeth;lateral teeth also clear except the 4th tooth is a trace or the 4th lateral tooth also clear;the fisrst keel smooth or existing granular;knob 4or 6 in carapace;body colour olive or dark green,dark copper;tarsus of the 5th pereiopod flat and shaped oar,bneadth under 2 in length or slight flat but not as sharped oar,breadth 2-2.5 in length;toe sogment of shaped oar,breadth 4.3 in length or toe segment shaped claw,short daw,breadth 5-5.6 in length in the base. There are no significant differences in morphology,of the mitten crabs in different water systems,therefore they belong to different populations.