In a “very high-temperature reactor” (VHTR), the Nb–V-modified 9Cr–1Mo creep strength enhance the ferritic (CSEF) steel which is the chosen material for fabrication of reactor pressure vessels and piping because of its excellent high temperature thermal and mechanical properties. In such CSEF steel weldments, the hydrogen-induced cracking (HIC) is a critical issue. In the present work, the different levels of hydrogen have been induced in P91 CSEF weld metal to study their effect on HIC. The HIC susceptibility of P91 steel welds has been studied by carrying out the tensile test and flexural test for the different level of diffusible hydrogen. The hydrogen levels in deposited metals have been measured by using the mercury method. The fracture tensile and flexural test samples have been characterized based on the field-emission scanning electron microscope (FE-SEM). It is concluded that higher the level of diffusible hydrogen in deposited metal, more is the susceptibility of P91 steel to HIC. The minimum flexural and tensile strength are 507.45 MPa and 282 MPa, respectively, for 12.54 ml volume of diffusible hydrogen in 100 g of deposited weld metal.