In today's economic globalization and financial liberalization processes, exchange rate, a main leverage meant to control a nation's macro economy, plays an increasingly important role in the national economic development. Upon China's accession to WTO in November. 2001, study of RMB exchange rate vitality becomes especially important in understanding the genesis of RMB exchange rate, its improvement, and its eventually internationalized free exchange process. This paper makes a comparative study, using GARCH model, of China and the US foreign-exchange market volatility, revealed special aspects controlling the genesis of RMB exchange-rate.