The present invention discloses a double diffused drain metal oxide semiconductor (DDMOS) device and a manufacturing method thereof. The DDDMOS device is formed in a substrate, and includes: a drift region, a gate, a source, a drain, a dielectric layer, and a conductive layer. The drift region includes a first region and a second region. The gate is formed on the substrate, and overlaps the first region from top view. The source and drain are formed at both sides of the gate respectively, and the drain is located in the second region. The drain and the gate are separated by a portion of the second region from top view. The dielectric layer is formed by dielectric material on the gate and the second region. The conductive layer is formed by conductive material on the dielectric layer, and overlaps at least part of the second region from top view.