Abstract: In order to reduce cost of transparent plastic welding and simplify its welding process, characteristic of thermoplastics absorbing 1 710 nm laser was utilized and welding experiment of transparent polymethyl methacrylate (PMMA) plastic without absorbent was carried out with this wavelength laser. Weld morphology, welding strength and physical phenomena in welding process were analyzed. Influence of laser heat input on mechanical properties and appearance of welded joints in this experiment was summarized by adjusting welding parameters. The experimental results showed that when heat input was 1.25 J/mm, shear force of PMMA welded samples was the largest and exceeded 20.55 MPa, but there was some burning points in the weld. When heat input was 1.11 J/mm, appearance of welded samples was ideal, and shear force of weld exceeded 17.8 MPa.Highlights: Laser welding of transparent plastics without adding absorbent was carried out and influence of laser heat input on welding strength and weld morphology was studied.