The invention discloses a double diffused drain NMOS device. An N-type buried layer is on a P-type substrate, and an N-type epitaxial layer is on the N-type buried layer; the N-type epitaxial layer has a P well and a drift region, a channel region of the double diffused drain NMOS device is between the P well and the drift region, and a silicon surface on the channel region is a gate oxide layer and a polysilicon grid electrode of the double diffused drain NMOS device; the P well has a doped P-type region and a source region of the double diffused drain NMOS device, and the drift region has a drain region of the double diffused drain NMOS device; the P well and the drift region respectively have a P-type doped layer which is respectively under the source region and the drain region; exhaust of the drift region is facilitated by the P-type doped layer, and a breakdown voltage is improved; the P-type doped layer under the source region has small influence on the device, and a threshold voltage almost has no change; drift region concentration of a current path does not decrease, no rise of conduction resistance of the device is guaranteed. The double diffused drain NMOS device is advantaged in that the breakdown voltage is improved without adding a mask, and cost does not increase.