Flame-retardant polyester microfiber/water-based polyurethane (PETMF/WPU) composites were prepared by dry solidification, alkali dewatering and post-finishing of sea island fiber nonwoven polyester (PET/COPET) with self-flame retardant water-based polyurethane (WPU) slurry containing impregnated phosphorus. The effects of self-flame retardant WPU slurry with different solid content of phosphorus on the flame retardant properties and mechanical properties of PETMF/WPU composites were analyzed and discussed. The flame retardant properties were characterized by cone calorimeter, limiting oxygen index and vertical combustion. The microstructure was characterized by scanning electron microscope. The thermal stability was characterized by TGA. The results show that when the solid content reaches 35wt%, the LOI value of PETMF/WPU composite reaches 31.7%, and the vertical combustion reaches V-0 grade. The composite can self-extinguishing and has no droplet generation in the combustion process, and its mechanical properties still meet the industry standard. The use of self-flame retardant materials containing phosphorus can reduce the release of harmful gases in the combustion process.