Abstract: For problems that voltage stability phenomenons caused by OLTC action and load dynamic characteristics are complicated and grasped hardly, the paper analyzed and researched influence of transformation ratio adjustment of OLTC on static voltage stability limit through Pmax-φ and Vcr-φ curves and critical transformation ratio corresponding to OLTC adjustment, so as to get conclusions as following: the Pmax-φ and Vcr-φ curves gradually shift upward with continuous increment of transformation ration of OLTC; the Pmax-φ and Vcr-φ curves gradually shift down with continuous decrease of transformation ration of OLTC; during adjustment of transformation ratio of OLTC, the adjustment range cannot exceed adjustment area determined by critical transformation ratio. The result of an example simulation proved that Pmax-φ and Vcr-φ curves can well describe influence of OLTC adjustment on static voltage stability limit.