Abstract: The fracture toughness of A517 GrQ steel plate was studied by using crack-tip opening displacement(CTOD) test.Different steel plate thicknesses,test temperatures and sampling locations along the thickness direction were selected in the tests.The results showed that the CTOD values of A517 GrQ steel decreased gradually from the surface to the core under the same temperature.With the increasing of specimen thickness(t),the CTOD eigenvalue(δ_m) of A517 GrQ steel increased first and then decreased slowly.It's suggested that the relationship formula of t and δ_mcould be proposed as δ_m=0.095t^0.5e^-0.009t1.17+0.65(1-e^-0.009t1.17).