The invention relates to a preparation method of a polyurethane foam immobilized microbe for treatment of azo dye sewage. The preparation method comprises the following steps: performing ultrasonic dispersion on polyester polyol, triethanolamine, water, methyl silicone oil, dibutyltin dilaurate and graphite felt powder after grinding together, then adding diphenylmethane diisocyanate (MDI), stirring until whitening, rapidly transferring, naturally foaming to obtain polyurethane foam, washing with distilled water for several times, then drying, preparing a lysogeny broth (LB) culture medium, putting the polyurethane foam into the LB culture medium, sterilizing together, cooling, then inoculating an immobilized microbe, namely a Stenotrophomonas maltophilia strain T-8, performing shaking culture and washing with the distilled water for several times for preparation. The polyurethane foam with the immobilized microbe prepared by the preparation method provided by the invention has a macroporous reticular structure, high specific surface area and hydroxyl and other groups, and can effectively immobilize the microbe and greatly improve the effect of decoloring azo dye.