Inordertopredictthetimingoftheoccurrenceofthesteelgirderoverallinstabili-ty and demonstrate the necessity of using lateral support during the loading process， the theoretical formula of the lateral-torsional buckling of the H-shaped steel girder in the el as-tic stage is derived by the energy approach under the condition of no lateral bracing sat any 2-point symmetrical transverse loading.Combined with the finite element model to verify the formula， it is found that the relative error between theoretical values and numerical val-ues is less than 3.5%， which indicates that the formula has a high precision.This formula and the current“Design code for steel structures”(GB 500017-2003) are conducted to calcu-late the critical moment for high performanceH-shaped girders，whose nominalyield strength are respectively 460MPa， 550MPa， 690MPa.The calculation results show that when two symmetrical loading is carried out， without any lateral bracing sin the middle span， overall instability phenomenon of the three kinds of steel girder will appear in the e-lastic-plastic stage and the critical moment is about 0.75 times of the ultimate moment.It is recommended to use the lateral bracing son the steel girder to carryout the constraint，which is expected to achieve the ultimate flexural strength.