Based on Wiener-Khinchin theorem,the coherence equation of broadband source has been derived and analysed.A precision setup base on Michelson interferometer configuration was made and the coherence characteristic curve of broad source with arbitrary spectrum profile was obtained accurately with modulation/demodulation technology.The coherence characteristics curves of superfluorescent fiber source(SFS),Fabry-Perot(FP) type and quantum well(QW) type superfluorescent diode(SLD) were investigated and compared respectively.The results agree with theory analysis well.It was found firstly that the coherence length of FP type SLD increases with inject current increasing,while the QW type SLD is on the contrary.