More than 30bending beams with rectangular cross-section and different thicknesses and heights were prepared from Q235steel.The specimen dimensions were about 240mm(length)×60mm(height)×70mm(thickness).Flaws were cut along its middle line with a wire cutter,with lengths ranging from 6to 35mm.Each specimen was tested with three-point bend loading,and a process curve was obtained between load and the displacement of the loading point,in order to analyze the fracture process when opening the crack.A deformation near the prefabricated crack was observed in the testing period,and the variation of the fracture characteristic parameters was analyzed for different sizes.For a comprehensive understanding of carbon steel fracture resistance behavior,its elasticity and plasticity were established by determining its Young′s modulus and Poisson′s ratio with an optical strain gauge.This gauge was also used for the loading process test.It was found that the fracture toughness varied with the dimensions,and the toughness of the elastic limit loading was almost constant.Using the relationship of crack resistance stress intensity factor and fracture criterion,the bearing capacity of the material structure could be estimated,which shows a good agreement with the experimental test data. More than 30bend beams with rectangular cross-section and different thicknesses and heights were prepared from Q235steel. The specimen dimensions were about 240mm (length) × 60mm (height) × 70mm (thickness) .Flaws were cut along its middle line with a wire cutter , with lengths ranging from 6to 35mm. Each specimen was tested with three-point bend loading, and a process curve was obtained between load and displacement of the loading point, in order to analyze the fracture process when opening the crack. A deformation near the prefabricated crack was observed in the testing period, and the variation of the fracture characteristic parameters was analyzed for different sizes. For a comprehensive understanding of carbon steel fracture resistance behavior, its elasticity and plasticity were established to determine its Young’s modulus and Poisson ’S ratio with an optical strain gauge. This gauge was also used for the loading process test. It was found that the fracture toughness varied with the di mensions, and the toughness of the elastic limit loading was almost constant. Using the relationship of crack resistance stress intensity factor and fracture criterion, the bearing capacity of the material structure could be estimated, which shows a good agreement with the experimental test data.