The invention relates to a method for forming a part isolating zone, firstly an oxidizing lining layer and a first silicon nitride layer are formed in turn on a silicon underlay, the oxidizing lining layer, the first silicon nitride and the silicon underlay are etched to form a groove, an insulating oxidizing layer is formed on the first silicon nitride layer, the insulating oxidizing layer can be filled fully in the groove; a second silicon nitride layer is formed on the insulating oxidizing layer, the second silicon nitride layer, the insulating oxidizing layer and the first silicon nitride layer are rubbed to remove the first silicon nitride layer and the oxidizing lining layer and form a shallow groove isolating structure. After the steps are finished, and because one silicon nitride layer is deposited on a silicon oxide layer, when the silicon oxide layer and the silicon nitride layer are rubbed, the speed for rubbing the silicon nitride is slower than that for rubbing the silicon oxide, thereby the depressed condition of the silicon oxide in the shallow groove can be improved after the rubbing process is over.