In this study,a kind of low carbon bainite metal powder cored wire was used for butt welding,and the effects of different welding heat inputs on the microstructure,tensile properties and impact toughness of deposited weld metals were investigated. The results showed that the microstructure of original weld（cover weld） and reheated zone in low carbon bainite deposited weld metals consists of granular bainite and quasi polygonal ferrite. The granular bainite content in the original weld metal and the reheated zone in the deposited weld metals first increases and then decreases with the increase of welding heat input. The yield strength and ultimate tensile strength of the deposited weld metals also increase first and then decrease with the increase of welding heat input,which is directly related to the change of the microstructure. The maximum yield strength and ultimate tensile strength of the deposited weld metals can be reached at the welding heat input of 17.9 kJ/cm,while the impact toughness decreases with the increase of welding heat input. The deposited weld metal at the heat input of 13.4 kJ/cm shows the best impact toughness at room temperature and -50 ℃,which is directly related to the fine grains with smaller heat input.