This article uses a new type of nitrogen-containing nickel-based flux cored welding wire as the experimental material to study the tensile properties and deformation mechanism of the deposited metal from room temperature to 900 °C. The results show that the tensile strength gradually decreases with the temperature. The plasticity gradually increases, but the lowest value appears at 700 °C, which is the phenomenon of intermediate temperature brittleness. M23C6 carbides begin to decompose at 700 °C. More carbonitrides are precipitated within the crystal with temperature. In the low-temperature zone (T≤600 °C), the main deformation mechanism is the unit dislocation a/2<110> cutting precipitation phase. In the medium-temperature zone (600 °C<T≤750 °C), initiation of Orowan bypass mechanism for dislocations. In the high-temperature zone (800 °C≤T≤900 °C), the slip and climbing mechanism of dislocation is the main deformation mechanism.