The invention provides a frequency synthesizer for an S-band wave observation radar. The frequency synthesizer comprises a first local oscillation generation module, a radio frequency generation module, a 740 MHz amplifying module and a second local oscillation generation module, wherein the 740 MHz amplifying module outputs two paths of signals; one path of the signals are connected to the radio frequency generation module, and the other path of the signals are connected to the second local oscillation generation module; the radio frequency generation module is connected with the first local oscillation generation module and the 740 MHz amplifying module; and the second local oscillation generation module is connected with the 740 MHz amplifying module. The frequency synthesizer has the advantage that three stable radio frequency signals are output after frequency synthesis is conducted on four output signals generated by a synchronous controller of the S-band wave observation radar, wherein the three stable radio frequency signals comprise one radio frequency signal provided for a transmitter of the S-band wave observation radar, and two local oscillation signals provided for an analog front end of the S-band wave observation radar.