In this paper, the authors propose two new formulas for the plastic buckling of plates as well as the plastic buckling of corrugated plates, one of which is called T-formula (isotropic tangent modulus formula) and another is nai icd Orthogonal Anisotropic Tangent Modulua Formula. The former which gives the lower limit of plas lc buckling stress of plates, corresponds to “Shanley load” in case of column instability, and G _t = E _t /2 (1-ν). The latter is obtained from a plane stress problem in which the yielded plate subjected to comp essive load is regarded as a orthotropic corrugated plate, and G _t = E E _t / E + (1+2ν) Et. These two formulas tabulated in Table 1 with other famous formulas, showed a satisfactory agreement with the test results (Fig. 10). The authors also established the general calculating method to obtain the ultimate strength of corrugated plates in plastic range (using τ-formula explained above) as well as in elastic range for design purposes, including the determination of all the rigidities of corrugated plate. Especially, the torsional rigidity D_xy , was checked by a test which coincided with the calculated value. The behavior of elastic buckling stress (σ) of orthotropic plates is also studied in this paper. Provided D_x , D_y =α D_x , H =β D_x and α =β² (where α= anisotropic coefficient for bending and β= anisotropic coefficient for torsion), it is shown in Fig. 7 that σ decreases gradually as βdecreases from 1 to 0 and the corresponding buckling mode also changes as σ varies.