As human beings explore the outer space, the demand for the nuclear sources in space missions is increasing. Almost all the existing space nuclear reactors have adopted the design of gas-cooled fast reactor, and the temperature feedback effect of the fuel of the small fast neutron reactor is different from that of the traditional pressurized water reactor. For the space fast reactors, they are designed to be compact and with a long operating lifetime to accomplish the long-term space missions. Due to the high-level enrichment of U-235 in the fuel, the Doppler effect of U-238 has little impact on the reactor reactivity. In the present paper, based on the design of the megawatt-class space gas-cooled fast reactor, the overall temperature feedback adjustment capability of the core, and the overall temperature coefficient of the core including fuel, structural materials, and coolant are investigated. The calculation results show that the temperature of the coolant has little effect on the reactivity. The temperature coefficient of the fuel is positive, and the structural material with a large negative temperature feedback coefficient. At the same time, the deformation of the fuel pellets due to thermal stress at high temperatures and the reactivity changes caused by the deformation are analyzed.