Due to the excellent corrosion resistance and small absorption interface of thermal neutrons, Zr has been widely used in nuclear industry. As an important manufacturing process, the welding of Zr is usually performed by manual tungsten inert-gas arc welding (TIG). Due to the low deposition efficiency of tungsten inert-gas arc welding (TIG), it is more suitable for thin plates. If this method is used for thick plates, it will increase the cost of time, manpower and material resources. Therefore, for thick plates, an advanced and efficient welding method is required to improve the welding quality and construction efficiency. In this paper, a combination of plasma arc welding (PAW) for root bead and tungsten inert-gas arc welding (TIG) for filling and cap beads was successfully developed for 20mm Zr-3 plate, with specifically designed clamp and gas shielding devices based on the welding characteristics of Zr. Different post-weld heat treatment was performed for the weld pieces. Moreover, the mechanical properties and corrosion resistance of welded joints were evaluated. The results demonstrates that welded joints which meet the requirements specified in code and standard and engineering requirements can be obtained by developed welding process and welding system; the influence of different heat treatment on mechanical properties and corrosion resistance of welded joints was not obvious.