The invention discloses a continuous laser device spectral line width measurement device based on an optical frequency comb. The continuous laser device spectral line width measurement device is characterized by comprising an optical frequency comb control module, an optical frequency comb seed source, an optical frequency comb spectrum broadening module, a continuous laser generating source, an optical beam combining module, an optical frequency selecting filtering module, a beat frequency detecting module and a signal reading module. The spectrum of the precisely-controlled optical frequency comb is broadened, output light of the precisely-controlled optical frequency comb and output light of the continuous laser generating source together enter the optical beam combining module, the light spots of two outgoing laser beams coincide, and then the two laser beams together enter the optical frequency selecting filtering module, two laser beams obtained through filtering pass through the beat frequency detecting module, the sizes of light spots are changed through shaping, and the light spots are concentrated on a detector, beat frequency signals are obtained through coherent combination, and the output spectral width of the continuous lasers to be measured can be contained through the signal reading module. The continuous laser device spectral line width measurement device is stable in structure and high in practicability, the measurement process is rapid and simple, and the output spectral width of one or more wave length continuous lasers can be obtained in real time.