Using small heat input,9 Ni steel were welded by arc welding with different welding parameters. The microstructure of welded joints were observed,and the tensile,bending,impact,hardness test on weld joints were conducted to study the effects of welding current,voltage and interlayer temperature on the microstructure and bending properties of welded joint. The results show that microstructure of the welded seam is mainly composed of austenite and precipitated phase,there are obvious liquefaction cracks in the welded seam with high welding current and voltage and without controlling the interlayer temperature,and granular bainite is found in the HAZ,the microstructure is composed of lath martensite with low welding current and voltage. The tensile,impact and hardness tests of the welded joints are all qualified with the two welding parameters. The impact energy,plasticity of the welded joints are slightly lower and poor and the hardness values of the HAZ is smaller with high welding current and voltage,and the crack propagates along the heat affected zone and leads to bending fracture with external stress. The welded joints with low current and voltage have good plasticity and qualified bending test.