The invention provides a key parameter determination method of a disconnector for a lightning arrester. The method comprises the following steps: 1) obtaining external surface leakage current of the lightning arrester under an extreme condition through artificial pollution test to determine long-time running current of the disconnector for the lightning arrester; and 2) obtaining internal leakagecurrent of the lightning arrester after aging through lightning impact aging test, and determining minimum working current I of the disconnector for the lightning arrester based on the external leakage current obtained through the artificial pollution test, I=k(I externalMAX+I internal), wherein the I externalMAX is the continuous running current of the disconnector for the lightning arrester, andthe I internal is the internal leakage current of the lightning arrester after aging. The method determines the continuous running current of the disconnector for the lightning arrester by utilizingthe leakage current of the lightning arrester obtained through the artificial pollution test, and determines the minimum working current I of the disconnector for the lightning arrester based on the leakage current of the lightning arrester obtained after lightning impact aging test, and can effectively and accurately determine key parameters of the disconnector for the lightning arrester.