We investigate the structure of yrast bands in the transuranium nuclei 242Pu and 244Pu in the framework of the projected shell model,which is a fully quantum mechanical and microscopic approach.It is found that an appropriate modification of the standard Nilsson spin-orbital parameters in the N =6 proton shell is necessary to correctly describe the high-spin backbending phenomenon in nucleus 244 Pu.In order to test whether this modification is correct,the same modified parameters are used to calculate the yrast band of its neighboring isotope 242 Pu.It is found that without this modification,a backbending will occur at spin I =20,which is not supported by the experimental data.