The invention provides near-UV excitation blue light fluorescent powder used fro a white light LED and a preparation method thereof. The chemical formula of the blue light fluorescent powder is Ca4-xZrGe3O12:xBi3+, wherein 0.01<=x<=0.4. The method includes the concrete steps that a calcium-containing compound, a zirconium-containing compound, a bismuth-containing compound and a germanium-containing compound are mixed with a cosolvent boron-containing compound to be calcined for 3-8 hours at the temperature of 1300-1400 DEG C and cooled to obtain the fluorescent powder. Non-rare earth ions are adopted as an activator, germinate without rare earth elements is adopted as a substrate material, and the activator and the substrate material are synergistically cooperated to obtain the blue light fluorescent powder Ca4-xZrGe3O12:xBi3+ (0.01<=x<=0.04). Emitted blue light is stable in color development, luminous efficiency is high, no rare earth elements are contained, and the high cost of the blue light fluorescent powder is lowered.