In order to investigate the effect of austenitizing temperature and holding time on the martensitic lath width and microhardness, the microstructures of China Low Activation Martensitic (CLAM) steel_(HEAT 0603A) specimens with different heat treatments were analyzed by scanning electron microscope (SEM), and the martensitic lath widths were gained. Besides, the microhardness was obtained by Vickers hardness tests. Based on these results, the relationship between microhardness and heat treatment was given. Taking all factors into consideration, quenching at 1253K for 30min was the optimum heat treatment condition for CLAM (HEAT_0603A). Further study and investigation, such as a series of verification tests etc., will be carried out in the near future.