The technology of frequency-conversion ranging in pulsed laser radar is proposed. Compared with traditional pulsed laser ranging, the technology of frequency-conversion ranging has the superiority of high speed and precision, which means that this technology has a broad application prospect. The theory of initiative and passive frequency-conversion ranging is introduced in detail. Emphasis is put on deriving the computing expressions and analyzing the working theory of this technology. Also, the restriction factors which affect its application in engineering are discussed.