Millimeter-wave technology is developing rapidly in recent years, and source modules are key components for millimeter-wave test instruments. A U-band quadruple-frequency source module was presented in this paper. Principles, design, simulation, fabrication of source module were described in detail. Input port of the source module was 3.5mm coaxial female connector and output port was standard WR19 waveguide port. Parallel coupled line bandpass filters were fabricated to suppress harmonics and obtain pure signal. Microstrip antipodal finline was fabricated to realize microstrip-to-waveguide transition. Test results showed that harmonic suppression was better than 60dBc and output power in frequency band of 44GHz~57GHz was between 6.3dBm and 8.2dBm. The quadruple-frequency source module had been successfully applied to millimeter-wave test instrument.