Due to the wide spectra, the conventional methods can not evaluate the beam quality of the whole supercontinuum (SC). A new factor SC-M2 is introduced. The spectra of supercontinuum is obtained by solving the generalized nonlinear Schrdinger equation by the using of split-step Fourier method. The spectral centroid is calculated based on second-moment method. The near field optical power distribution of the supercontinuum source is obtained by the using of finite element method. After free space propagation, the far field distribution is obtained. Founded on the near field, far field and spectral centroid, the SC-M2 factor is defined to evaluate the beam quality of supercontinuum source as a whole. With this factor, the beam quality of supercontinuum source can be evaluated comprehensively and comparison among different supercontinuum sources can be made.