Abstract: FH36 ship steel plates were welded using E81T1-K2 flux cored wire (FCW) with different heat inputs (12.98, 15.88, 18.47, 20.37, 22.59 kJ·cm-1 ). The effects of heat input on the microstructure and low temperature impact toughness of the deposited metal were studied. The results show that the low temperature impact toughness of the deposited metal increased first and then decreased with the increase of heat input, and displayed the maximum value of 79 J when the heat input was 18.47 kJ·cm-1. With the increase of heat input, both the side plate ferrite content (area fraction) and the grain boundary ferrite content decreased first and then increased, but the acicular ferrite initially increased and then decreased and showed the maximum of 85.2% when the heat input reached 18.47 kJ·cm-1.