Abstract: The limitations and problems of evaluation of welding procedure specification(WPS) of steel box beam with impact test were analyzed.It is necessary to use the crack tip opening displacement(CTOD) test to evaluate WPS of steel box beam.The CTOD test was presented.Two WPS used for the fabrication of steel box beam of back-gulf Bridge in Hong Kong-Shenzhen Western Corridor was designed and evaluated with CTOD test according to BS7448.The results are as follows:1) The values of CTOD fracture toughness in welded joints of submerged arc welding(SAW) are higher.The welding procedure specification of SAW can be directly applied to the fabrication of steel box beam.2) The values of CTOD in welded joints of shielded metal arc welding(SMAW) are lower.Hence the welding procedure specification of SMAW should be amended.It is found by scanning electron microscope that there are gas holes and micro-cracks and inclusion and harmful sulphur in the welding position.