Abstract: In order to explore the influence of open holes on the monotonic mechanical properties of Q355B cold-formed high-strength steel plate， 8 groups of test samples were designed for each thickness， using 2 mm and 3 mm thick specimen steel plates， and 3 parallel samples were set up for mechanical test tests in each group. Then the influence of the thickness of the specimen， the number and type of holes on mechanical properties of the specimen were discussed by analyzing the stress-strain curve of the specimen. On this basis， the finite element analysis software was used to create a model of an open-hole specimen. The model was then compared with the results of the material properties test to validate its accuracy and reliability. This process is convenient for subsequent development and research. The test results show that the unopened specimen has an obvious necking phenomenon near the fracture of the open-hole specimen， and the failure and stress concentration phenomenon occur near the hole of the open specimen. Under the premise of the same type of open-hole specimen， the greater the thickness of the specimen， the stronger the capacity of resisting the damage of the open-hole defect； the greater the thickness， the better the mechanical properties such as ductility and energy dissipation capacity； With the increase of the opening diameter， the strength index and deformation ability of the specimen were reduced， but its influence on the elongation was increased； Specimens with hole openings arranged along the direction of external force had a better energy dissipation capacity than specimens with hole openings perpendicular to the direction of external force.