With the precipitation strengthening phase of ternary compound γ′-Co3(Al,W), the Co-Al-W superalloy is a novel cobalt-based superalloy. In order to study the phase composition and cracking behavior of Co-8.8Al-9.8W-0.2B cladding layer on the 304 stainless steel with TIG welding. The phase composition and relative content of elements at different positions in cladding layer were studied with thermodynamic simulation calculation of JMatPro software. The results show that the phase composition should be the same in different position of cladding layer, but the content of those phases are difference. Based on the analysis of the phase composition and content of the elements in the cladding layer, the surface cracks of cladding layer are hot cracks, which are the results of thermal stress, the phase transformation stress and Laves phase.