The invention provides a preparation method of modified nitrile rubber. The method comprises the following steps of: A, plasticating chloric ether rubber, and adding a reinforcing filler, an antiaging agent and a plasticizer to mix so as to obtain masterbatch of chloric ether rubber; B, dispersing the masterbatch of chloric ether rubber in an organic solvent to form chloric ether rubber latex; C, plasticating the nitrile rubber, and adding a reinforcing filler, an antiaging agent and a plasticizer to mix so as to obtain masterbatch of nitrile rubber; D, blending masterbatches of chloric ether rubber and nitrile rubber, adding an acid absorber, an activating agent and a vulcanization accelerator to mix, and then adding a vulcanizer for open mill to obtain the modified nitrile rubber. The invention further provides modified nitrile rubber prepared by the preparation method. In the preparation method of modified nitrile rubber provided by the invention, first, chloric ether rubber is prepared as latex which is easy to disperse from nitrile rubber, so that modified nitrile rubber which is uniformly dispersed, and good in processing performance, low temperature and weather ability is prepared.