Dissimilar steel welded joints are common joint types for welding structures such as boilers and pressure-bearing equipment.Through the test research on the welding joint of 20MnMo and SA-299B,the CHE557R（GB/T5117 E5515） electrode was selected for the oblique y crack test. The welding test plate,the post-weld heat treatment and the joint mechanical property test,the hardness test and the metallographic phase were carried out according to the proposed welding process. The test results show that 20MnMo and SA-299 have good welding performance;the weld microstructure is mainly acicular ferrite +pearlite structure,and the parent materials of 20MnMo and SA-299B are pearlite+ferrite,the heat effect zone is mainly bainite structure,and the carbides in the 20MnMo side heat affected zone are precipitated,showing different regional differences in joints:joint hardness from 20MnMo base metal and heat affected zone,weld seam,SA-299B thermal shadow zone and the mother material also shows non-uniformity;tensile strength,bending perf-ormance and impact toughness of welded joints meet the requirements of NB/T47014 "Welding Process Assessment for Pressure Equipment". However,the impact absorption work of the 20MnMo side heat affected zone is relatively low,which is in good agreement with the microstructure of the region. It shows that the toughness reserve of 20MnMo and SA-299B dissimilar steel welded joints is weak in the 20MnMo side heat affected zone,which has good guiding significance for engineering application of 20MnMo and SA-299B.