Abstract: F.B.Alt and others have designed control limits for The T² Charts when the number of subgroups being small. This article presents control limits for the\sqrt|S| charts on the same condition,derive the formulas of retropective test and trial control limits\sqrt|S| for 2-dimensional case:Retrospect:\sqrt\left|S^(h)\right|=\frack F((2 n-4),(k-1)(2 n-4))(k-1)+F((2 n-4),(k-1)(2 n-4)) \sqrt|S|,Trial: \sqrt\left|S^f\right|=F((2 n-4), k(2 n-4)) \sqrt|S|, where k is the number of subgroups, each of size n. S^（h） and S^f are covariance matrix for eachsubgroup and a future subgroup, respectively. \sqrt|S|=\frac1k \sum_h=1^k \sqrt\left|S^(h)\right|. Hence we may determineupper and lower control limits for \sqrt\left|S^(h)\right| and √|S^f|charts, respectively.