Abstract: To study the effect of thick plate＇s original welding thickness and specimen location on the fatigue crack growth rate, the fatigue crack growth tests for 30 fatigue testing specimens made from 14MnNbq steel with five variables of original welding thickness(i.e.40 mm,50 mm,60 mm,80 mm and 100 mm) were conducted. Mathematical Statistics was used to deal with the test data, by this means the da/dN-ΔK curves and the parameters for Paris formula were obtained under a given confidence. The results show that, the fatigue crack growth rate increases along with addition of original welding thickness. Besides, considering the effect of the location of specimen, the fatigue crack growth rates of external specimens are faster than those of internal.