0.12 mm thick films of thermoplastic polyurethane (TPU) are welded using laser transmission welding technology. The effect of main welding parameters including laser average power, welding speed on welding quality is investigated. The results show that using Clearweld resins, the color of welding seam is similar to parent material’s, and colorless welding is obtained. The experimental results show that at the welding speed of 100 mm/min, with increasing of laser average power from 0.31 W to 8.11 W, the seam width increases from 0.86 mm to 4.10 mm. When the laser average power is lager than 2.30 W, the material is decomposed in the weld seam. When the laser average power is lager than 7.15 W, the material is ablated. And the peeling strength is all more than 1.3 N/mm during the laser average power from 0.6 W to 5.89 W. Adjusting welding speed and fixing the laser average power, parameter window for laser transmission welding is obtained. The results show that with the matching of laser average power and welding speed, the welding speed can be increased by the premise of guarantee of weld seam quality.