In order to guide the rolling process in industry, the effect of heat treatment temperatures and holding times on the structure and mechanical properties of the hot-rolling plate of Fe-42% Ni (4J42) was studied. The results about the metallography show that with the increasing of the heating temperature, the grain sizes of all the samples grow. Furthermore, the phenomenon of twin crystal in grains is more and more obvious. The mechanical tests show that with the increasing of the temperature and the holding time, 4J42’s tensile strength declines; when the heat temperature is 1000°C, holding times have little effect on its elongation; when the holding time is less than 8min, the hardness of 4J42 declines at different temperatures. Combine the requirements in industry with the experiment results, we found that 1000°C, 8min is appropriate to the rolling process of 4J42 alloy.