The present invention relates to a method for producing a composite structure comprising fiber reinforced material by means of vacuum assisted resin transfer molding, where fiber material is impregnated with liquid resin. The method comprises an evacuation process of a mold cavity by initially providing an under-pressure in a part of the mold cavity in order to provide a first vacuum front having a first pressure gradient oriented towards a first side of the forming structure, and a second vacuum front with a second pressure gradient oriented towards a second side of the forming structure, and controlling the first vacuum front and the second front to move towards the first side and the second side of the forming structure, respectively.