The influences of the flux KCl or KF on the XRD spectra, cell parameters and crystal appearance, and spectral properties of the phosphor LaMgB5O10:Ce3+, Mn2+ were studied. The results indicate that when 4.2%, 8.6%, 12.8% KCl and 5.3%, 10.5% KF are respectively added into phosphor (La0.85Ce0.15) (Mg0.9Mn0.1)B5O10, Compared with the normal card of JCPDS (No 35-120), the intensity of XRD spectra is enhanced, the values corresponded to 17/28, 18/28, 16/28, 18/28 and 2/28 and the cell parameters diminish because of the flux KCl and KF. The use of 5% KCl a fraction of Cu monocrystals are observed in the phosphor. There are six hexagonal crystal-faces and eight triangular crystal-faces representing crystal-face index {100} and {111}. When 15% KCl is added to the phosphor, law of crystal plane and self-regulaton are formed, the emission intensity of Ce3+ 5d - 4f (F-2(5/2), F-2(7/2)) and Mn2+ ((4)G and S-6) increases by 3.41 times and 2.36 times respectively.