Abstract: hydrogen embrittlement index (1%) of welds and heat affected zone(HAZ) of C-Mn steel welded joints are studied by means of smooth and notched tensile specimen. Meanwhile metallogragh and micro, macro fractogragh of the specimen are analysed with SEM, TEM and AES methods Experimental results have verified that the 1% of weld metal is the lowest, parent metal is the next and the HAZ metals with its peak temperature(Tmax℃) in the range 1100℃-1300℃ has a highest 1% among other parts of a welded joint, so it can be considered as a weakest region to hydrogen embrittlement.