The influence of reactor pressure on GaN layers grown by hydride vapour phase epitaxy (HVPE) is investigated. By decreasing the reactor pressure from 0.7 to 0.5atm,he GaN layer growth mode changes from the island-like one to the step flow. The improvements in structural and optical properties and surface morphology of GaN layers are observed in the step now growth mode. The results clearly indicate that the reactor pressure, similarly to the growth temperature, is one of the important parameters to influence the qualities of GaN epilayers grown by HVPE, due to the change of growth mode.