The invention belongs to the field of mold erecting and pouring technologies for drainage ditches for airport construction engineering, and discloses a method for forming trapezoidal drainage ditches by means of pouring on the basis of adjustable groove forming molds. The method has the advantages that by the aid of the method, the problems of incapability of recycling mold erecting devices and the like, long construction periods, difficulty in guaranteeing the construction quality of existing drainage ditches and the like due to variable sections of most existing grooves and structural limitation of the existing mold erecting devices and existing excavator bucket devices when the existing grooves of the existing ditches are constructed can be solved; grooves are subjected to one-step excavation and one-step mold erecting pouring by the aid of adjustable excavator bucket devices and the groove forming molds, the adjustable groove forming molds comprise mold erecting supports, wood mold plates and hollow steel pipes with rectangular sections, and every two corresponding wood mold plates cling to the inner side wall of the corresponding groove of the corresponding drainage ditch, can be supported by the corresponding mold erecting supports and can be tensioned by rotary components; slope ratios of the mold erecting supports of the adjustable groove forming molds can be adjusted according to change of slope ratios of the grooves, the molds only need to be simply adjusted without mold processing, accordingly, the molds are high in utilization rate as compared with the traditional integral welded mold erecting supports, and adjustment procedures are simple.