Let N be the set of {1, 2, , ...,m}, [x, y] denote the set of [x, x + 1, ..., y], where 1 \leqslant x,y \leqslant m. Given two permutations sA and sB of a set N, A 2-tuple of intervals ([x_1 ,y_1 ],[x_2 ,y_2 ]) is called common intervals if \sigma _A ([x_1, y_1]) = \sigma _A([x_2, y_2]). In this paper, we propose a sufficient and necessary condition for a 2-tuple of intervals to be common intervals. Based on these conditions, we present a generic algorithm that finds all common intervals of these two permutations.