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In the design of most bridge girders with composite girders composed of steel–concrete composite plate girders, an opening in the steel girder is often used to provide passage for utility ducts and pipes. This results in significant savings in material and construction costs. So it is necessary to study the effect of an opening in the web steel on the behavior of the composite girders if the designer wishes to provide adequate opening in the structural elements without reducing its load carrying capacity. In this paper, a non-linear finite element analysis has been done to analyze the deflection in the steel section and internal stresses in the concrete slab for continuous composite girders with a single rectangular opening in the steel web. ANSYS computer program (version 15) has been used to analyze the three-dimensional model. The reliability of the model was demonstrated by comparison with experimental results of continuous composite beams without an opening in the steel web carried out by another author. The parametric analysis was executed to investigate the width, height, and position of the opening in one span on the behavior of a composite girder under vertical load. The results indicated that when the width of opening is less than 0.05 of length of a single span and the height is less than 0.15 of the steel web, the deflection and internal stresses increased less than 10% comparing to continuous composite girders without an opening.