The present disclosure provides a DMOS device with a junction field plate and its manufacturing method. A drain region is located on a surface of a semiconductor substrate. A source region is located in the semiconductor substrate at a bottom of a first trench. A gate electrode is located at the bottom of the first trench. The junction field plate improves an effect on reducing surface resistance. At the same time, a depth of trenches in the DMOS device may be reduced, and thereby a depth-to-width ratio of the device is reduced, improving the feasibility of increasing a voltage resistance level. Both the source region and the drain region in the DMOS device are led out on a same surface. A second doped polycrystalline silicon layer includes a first doped sublayer and a second doped sublayer with different conduction types.