The machining precision of bending machine is one of the most important performance indicators, due to the structure form of the sheet bending machine, the manufacturing precision of the bending machine itself, the manufacturing precision of the mould, the performance of the processed sheet and the uneven performance of the machine tool, there are inevitably angular errors, straightness errors and side length errors in the machined work-piece. The existence of sheet metal processed error affects the subsequent assembly, increases the workload of trial-repair molds and post-forming calibration, increases the development cycle of products and restricts the further promotion and application of automatic bending. A PBB type Numerical Control (NC) sheet bending machine is taken as the research object. Combined with strain electrical measuring technique and finite element (FE) simulation, the bending machine was optimized and improved, based on this, a PBH type was experimentally produced. The research results have important practical significance for improving the bending precision and reliability of sheet metal, improving the competitiveness and practical added value of products.