The invention discloses a preparation method of a soft floor. Polyether is pretreated to obtain flame retardant polyether, the flame retardant polyether and liquefied MDI are uniformly mixed, and thenfed into a mold through a casting machine, the injection time is 15-20 min, the mold is sprayed with a mold release agent before use, after thermal insulation placement in the mold for 30 to 60 minutes, a formed floor mat is taken out from the mold, after trimming of burrs, rolling for and venting, and sizing, a TPU film is compounded to obtain the product, and the used mold is washed with a cleaning agent for recycling. The soft floor has good anti-skid performance and good environmental friendliness, each test index satisfies national standards, and the soft floor has simple manufacturing process and low cost.