The invention relates to a fluoborate and a crystal containing rare earth ions, and a preparation method thereof. The chemical formula of the fluoborate is (Ca1-xRex)5(BO3)3F1-5xO5x, wherein x is more than 0 and less than 0.2; Re<3+> is Sc<3+>, Y<3+> or the rare earth ions; and the rare earth ions are La<3+>, Ce<3+>, Pr<3+>, Nd<3+>, Sm <3+>, Eu<3+>, Gd<3+>, Tb<3+>, Dy<3+>, Ho<3+>, Er<3+>, Tm<3+>, Yb<3+>, or Lu<3+>, or mixture of the rare earth ions. A flux method is adopted to grow a fluoborate crystal with high quality and large size. The crystal meets the requirement of blue green light wave-band laser frequency conversion, and can be used for manufacturing nonlinear optical devices. A monocrystal doped with rare-earth laser activated ions can be used for manufacturing laser-nonlinear multi-functional optical devices; and lasers manufactured by the crystal can be used in the fields such as spectroscopy, biomedicine, military, and the like.