Abstract: To solve the fusion welding problem of K4951 alloy is the key to realize the development of a new generation of aero-engine casing. Since the K4951 alloy contains the high content of refractory elements and the weldability is poor, this study designed seven kinds of welding wires by adjusting the precipitation-strengthening elements and solid-solution strengthening elements according to the composition characteristics of the alloy. The effects of alloying elements on crack sensitivity and creep properties of the welding joints were analyzed by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), electro-probe microanalyzer (EPMA) and thermal-calc software. Results show that when the content of B was increased to 0.04%, the crack sensitivity of the joint was significantly increased, and the weld metal is fractured. Increasing the Nb content can improve the healing ability of the liquid film in grain boundary, which can reduce the welding sensitivity of welding samples, and increase the creep life of joints from 15 h to 41 h. Reducing the content of Cr and Mo can increase the crack sensitivity of the alloy to a certain extent and increase the creep life of the joint. Increasing Al content and regulating the Nb, Cr, Mo and other elements can effectively inhibit crack formation and improve the high-temperature service performance of the welding joint. The results of this study can provide an important reference value for the subsequent research on weldability of precipitation strengthened nickel-based superalloy.