To estimate the currency composition of China's foreign exchange reserves and assess its effectiveness of management, the constrained least square method and variance sensitive analysis are utilized, respectively. Based on portfolio accounting identities, the change of foreign exchange reserves was decomposed into the net purchase change and the non-purchase change. The newly constructed non-purchase change was used to estimate the latent currency composition. Empirical results show that by the end of 2015Q1, China held about 63.6% of its reserves in the U.S. dollar, 19.6% in the euro, 3.09% in the Japanese yen, 4.89% in the pound sterling, 2.22% in the Canadian dollar, 2.03% in the Australian dollar, and 0.09% in the Swiss franc. Although the currency composition kept relatively stable, more attention had been paid to the emerging international currencies. China decreased the U.S. dollar share during the subprime crisis, while resorted to the portfolio rebalance strategy since 2011. The euro share and the pound sterling share declined during the European sovereign debt crisis. The first derivative of the U.S. dollar was positive while those of other currencies were negative before 2014Q3, and vice versa after 2014Q4. In general, the currency composition management  of China's foreign exchange reserves was effective.