The invention relates to the technical field of warp knitting machines, in particular to a warp knitting machine left wallboard positioned welding device and an application method thereof. Two holes 1, an edge 1, an edge 2 and an edge 3 are arranged on a substrate 2 of the warp knitting machine left wallboard positioned welding device; a hole 4, an edge 4, an edge 5, an edge 6, an edge 7 and an edge 8 are arranged on a substrate 3; a limiting base is formed by welding a plate 1 and a plate 2; the plate 2 is vertically arranged on the plate 1, and is parallel to an edge 9 of the plate 1; the plate 1 is provided with a round hole matched with a positioning ring; the plate 2 is provided with a hole 6 for forming a handle; and the positioning ring takes the shape of a round pipe, and is matched with the round hole for positioning the circle center of an arc 1 on a bent plate 1 on a left wallboard of a warp knitting machine or the circle center of an arc 2 on a bent plate 2. The warp knitting machine left wallboard positioned welding device replaces a cutting machine marking scheme, reduces the requirements on cutting equipment, can fully use traditional equipment for production, reduces the production cost, replaces a manual line drawing scheme, improves the positioning precision and the production efficiency, and reduces the machining difficulty.