看一下FED的介绍

http://www.federalreserve.gov/monetarypolicy/openmarket.htm

Open market operations--purchases and sales of U.S. Treasury and federal agency securities--are the Federal Reserve's principal tool for implementing monetary policy. The short-term objective for open market operations is specified by the Federal Open Market Committee (FOMC). This objective can be a desired quantity of reserves or a desired price (the federal funds rate). The federal funds rate is the interest rate at which depository institutions lend balances at the Federal Reserve to other depository institutions overnight.
The Federal Reserve's objective for open market operations has varied over the years. During the 1980s, the focus gradually shifted toward attaining a specified level of the federal funds rate, a process that was largely complete by the end of the decade. Beginning in 1994, the FOMC began announcing changes in its policy stance, and in 1995 it began to explicitly state its target level for the federal funds rate. Since February 2000, the statement issued by the FOMC shortly after each of its meetings usually has included the Committee's assessment of the risks to the attainment of its long-run goals of price stability and sustainable economic growth


更详细的介绍文章

http://www.federalreserve.gov/pubs/bulletin/1997/199711lead.pdf

公开市场操作影响的是国库券的利率，为啥联储能设定银行间的联邦基金利率目标呢？

是因为有传导机制，国库券利率能影响联邦基金利率吗？————公开市场操作影响的是联邦基金利率，美联储具有公开市场操作（债券）的货币政策工具，美联储设定自己的目标利率，并依靠公开市场操作去左右联邦基金市场利率靠近自己设定的目标。