To investigate the destruction characteristics of intact structural loess under loading conditions, triaxial shear tests are conducted on Q2 intact loess. Based on the experimental results, a structural variable parameter m of soil is defined, which can consider the spherical stress, deviatoric stress, matric suction and other factors. By means of method for calculating the structural parameter m based on the experiment, the relationships among shear strength parameters c, and structural parameter m are found out, the curve equations of m with c, are deduced, respectively. By introducing the curve equations into Drucker-Prager (D-P) criterion, a modified yield criterion applicable to Q2 intact loess is established. The modified yield criterion can consider the structural effect of intact Q2 loess and describe the structural characteristics of loess very well. Besides, the yield surface reflecting the impact of structural parameters is drawn. The rationality of the modified yield criterion is verified by comparing the results of the modified yield criterion with those obtained from the triaxial tests.