The invention provides a preparation method of laminar plasma of single crystal diamond, and belongs to the technical field of single crystal diamond preparation. In the preparation method, by regulating and controlling fluid characteristics of the plasma, a stable laminar plasma boundary layer is constructed so that the single crystal diamond can grow stably on a large-sized substrate, which avoids problems such as poly-crystallization and small-sized substrate of the current single crystal diamond prepared through direct current plasma deposition. The preparation method has the advantages that a way to stably prepare the single crystal diamond by utilizing large-sized seed crystal is provided so that size of a stable growing region of the single crystal diamond reaches 7cm along the direction of a motion axis of the plasma, and meanwhile poly-crystallization on the single crystal growing surface is effectively inhibited.