The invention relates to a method for erecting a cable-stayed bridge steel truss in a marine environment. The method for carrying out steel truss erection in the marine environment comprises the following steps that small-section full-welded steel truss beams are manufactured, the beam falling position on an erection pier is acquired, large-section assembling is conducted on the small-section full-welded steel truss beams on a transport ship so as to form an assembled steel truss beam, the assembled steel truss beam is mounted on the beam falling position of the erection pier, and section buttjoint and closure are conducted on the assembled steel truss beam. According to the method for carrying out steel truss erection in the marine environment, by means of full-welding manufacturing of small sections in a factory and factory full-span assembly, industrial degree is high, quality is easier to guarantee, on-site steel truss girder assembling construction is effectively reduced, field construction risks are reduced, pollution to the environment caused by field welding and coating construction of the steel truss beam is reduced, and the method is green and environment-friendly.