In the study of lodging resistance of wheat stalk, a culm model with varying stiffness was established from wheat stalk by the variation of structural parameters, such as the Young’s modulus, inertia moment, the length of the internode, load and so on, in different internodes along the stalk height, and its critical load was analyzed by using initial parameter method. With tests performed on the wheat variety of Jinnong 190 in the milk stage, the structural parameters were obtained in different internodes. Based on the proposed model, the critical load was estimated and the safety factor was concluded as 1.97, which showed Jinnong 190 had a better ability in lodging resistance. The local bucking analyses showed that the Brazier buckling was hard to occur in the internodes of Jinnong 190 with the effects of its self weight and the tip weight.