The preoxidation of mesophase pitch fiber was simulated by means of thermo gravimetric analysis. Then, the radial deformation behavior and self-bonding process of pitch fiber on hot press were studied through thermal mechanical analysis. And the microstructure of self-bonding pitch fiber boards and self-bonding carbon fiber boards was analyzed with scanning electron microscopy. When the oxidation weight gain was 2.1%, the radial deformation rate of pitch fiber was 36%, which indicated that the pitch fiber was easy to be processed. Moreover, the surface of self bonding board was smooth and the contact surfaces of fibers were closely bonded. When the oxidation weight gain was 1.3%, the pitch fiber was molten for the destroying of microcrystal orientation and unable to be processed. When the oxidation weight gain was above 3.3%, the radial deformation rate of pitch fiber was small and the self-bonding ability of pitch fiber was poor.