In this paper, the line shapes of the coherent and incoherent output of a three-level (E3>E2>E1) quantum frequency converter have been calculated. The conversion between two optical frequencies, that between an optical and a microwave, and that between two microwaves are discussed. There are two types of operation of the three-level frequency converter. In type I the pumping frequency ～1/?(E2—E1), the frequency of the applied signal ～1/?(E3—E2), and the frequency of the output ～1/?(E3—E1). In type II the pumping frequency ～1/?(E3—E2),the frequency of the applied signal ～1/?(E2—E1), and the frequency of the output ～1/?(E3—E1). It has been shown that for the conversion between two optical frequencies, type Ⅱ is better.