Pressure vessel of gasifier is usually made of ASME specification material SA-387GR11CL2 plate. Due to the specific requirements of working conditions and service performance, the medium temperature mechanical properties of the pressure vessel are generally specified. In a gasifier project of DBC,the tensile strength of material and welding joints SA-387GR11CL2 plate at 427 ℃ should be not less than 450 MPa. Whether the material and welding joints could meet the relevant technical requirements after series of welding and heat treatment is the main manufacturing difficulty of this product. The effect of welding process and heat treatment specification on the properties of SA-387GR11CL2 materials and welding joints was studied by series of welding and heat treatment process tests analyzed with larson-miller parameters,and the heat treatment process test of the head was especially carried out. Reasonable welding process and heat treatment specification of pressure vessel of gasifier reactor,quench room and head were worked out.