This paper presents a numerical study for lateral distortional buckling of I-plate girders (LDBIPGs) by using the general-purpose finite element package ABAQUS (version 6.13) software. 3-D finite element (FE) models for simply supported IPGs subjected to two cases of loading are built. The first case of loading was uniform end moment that was introduced by a couple of forces applied at the top and bottom flanges of the IPGs. The second case of loading was a concentrated load at the shear center in the mid-span. First, shell finite element models are validated by comparing the FE critical bending moment (𝑴𝒄𝒓,𝑭𝑬) by the critical bending moment in EC3 code (𝑴𝒄𝒓,𝒐,𝑳𝑻𝑩). The results indicate that the 𝑴𝒄𝒓,𝑭𝑬 was in good agreement with 𝑴𝒄𝒓,𝒐,𝑳𝑻𝑩. Secondly, a preliminary analysis is conducted to the relative girder slenderness (𝜆) where the LDB too place. Finally, a parametric study is carried out on simply supported IPGs regarding to the span length, the flange cross-section dimensions and the thickness of the web. The results showed that increasing the length of girders decreases 𝑴𝒄𝒓.𝑭𝑬 and increase in the bending coefficient factor (𝑪𝒃). Also, decreasing in the web plate slenderness ratio (𝒉𝒘𝒕𝒘⁄) works on increasing in 𝑴𝒄𝒓.𝑭𝑬 values and 𝑪𝒃. The results also showed that the increasing in the thickness of flange increases 𝑴𝒄𝒓.𝑭𝑬 and increase the value of 𝑪𝒃 with small value. As a result of parametric study, the mean value and standard deviation of 𝑪𝒃 for LDB mode are 1.16 and 0.08 respectively for 𝝀 limits (90:130). For 𝝀 limits (131:175), the mean value and standard deviation of 𝑪𝒃 are 1.27 and 0.03 respectively. As for 𝝀 limits (176:221), the mean value and standard deviation of 𝑪𝒃 are 1.32 and 0.02 respectively.