In order to solve the problem of poor alkali resistance of flame retardant waterborne polyurethane in impregnation applications, the alkali resistance of flame retardant waterborne polyurethane was improved by introducing flame retardant silicone oil, a series of flame retardant waterborne polyurethanes with alkali resistance were synthesized, and it was prepared into flame retardant microfiber bass by wet immersion, and then its alkali resistance, flame retardant, mechanics and quality properties were tested, and the process formula of flame retardant microfiber bass with better comprehensive performance was determined by the flame retardant impregnated phosphorus and nitrogen type flame retardant in the finishing process. The results show that the introduction of flame retardant silicone oil can effectively improve the alkali resistance of flame retardant waterborne polyurethane and flame retardant microfiber bass. With the addition of flame-retardant phosphoryl-containing glycol, the horizontal combustion rate of microfiber bass decreases from 121.37 mm/min to 61.15 mm/min, which is 49.62% lower than that before flame retardant, and the LOI increases from 18.8% to 23.8%, which is increased by 26.60% compared with that before flame retardant. Through flame retardant finishing with phosphorus and nitrogen impregnated flame retardants, LOI can be up to 33.4%. It provides a new idea for the preparation of alkaline-resistant flame-retardant microfiber bass.