Fracture surface observations and statistical deriving are applied for investigating the random critical fracture toughness values of China grade B cast steel wheel. Results reveal that: the crack grows to show fabric like stripes along the growth direction with few of dimples. Cleavage flowers appear under higher magnification. Cracked structural damage process is verified with few of plastic dissipation. At the same time, code based evaluated results indicate that significant scatter exists for the toughness values. Lognormal modeling is constructed appropriately with a comprehensive statistical comparison method. It is verified that random characters and quantitative measurements have been well depicted for the present critical fracture toughness values.