A manufacturing method of an LDMOS device comprises: obtaining a wafer formed with a doped region having a first conductivity type, wherein a top buried layer is formed inside the doped region having the first conductivity type, and a field oxide insulation layer structure is formed on the top buried layer; disposing a trench on the doped region having the first conductivity type, wherein the trench extends to the top buried layer and the field oxide insulation layer structure such that a portion of the top buried layer is removed; injecting an ion of a second conductivity type to form a well region below the trench; and forming a doped source region in the well region. The first conductivity type and the second conductivity type are opposite conductivity types.