A laterally diffused metal oxide semiconductor device and a manufacturing method thereof. The device includes: a substrate of a second conductivity type; a drift region arranged on the substrate and of a first conductivity type; a source region of the first conductivity type; a drain region of the first conductivity type; and a longitudinal floating field plate structure arranged between the source region and the drain region and including a dielectric layer arranged on an inner surface of a trench and polysilicon filling the trench. The trench extends from an upper surface of the drift region downward through the drift region into the substrate. At least two longitudinal floating field plate structures are provided, and at least two of the longitudinal floating field plate structures are located at different positions in a length direction of a conductive channel.