Abstract: Hohlraum physics is fundamental to the indirect drive inertial fusion. The ultimate goal of laser-driven hohlraum is to create a radiation environment that ablatively implodes a capsule to ignite and burn. To obtain high fusion yield with minimum laser energy, the hohlraum radiation drive must meet both the high X-ray conversion and excellent uniformity. By optimizing the hohlraum structures and materials, the hohlraum performance could be improved in flux intensity, uniformity and spectrum. The hohlraum physics study focuses on the laser propagation through the underdense plasma, x-ray conversion by the laser interacting with the high-Z material and X-ray heating of high-Z walls. All of these issues are important for understanding the hohlraum. On the Shenguang-Ⅲ prototype laser facility, extensive experiments have been performed to characterize laser-heated hohlraum. We have demonstrated good understanding of the hohlraum energetics and radiation feature. Experimental study on vacuum hohlraum energetics obtains the scaling of the scattered light and radiation temperature with laser energy and hohlraum size. Gas-filled hohlraum impedes the motion of ablated wall plasma with the low-density, low-Z gas plasma, and exhibits a reduction of Au M-band flux that might adversely preheat the capsule. Several quantitative studies that concentrate on the specific regions inside the hohlraum have been performed. The laser spot movement with different flux limiter according to electron heat conduction has been investigated. The movement of laser heated corona plasma could be controlled by varying initial gas density. The ratio of the X-ray emission between the laser spot and the reemitting wall was measured in the same shot, which might contribute to the optimization of the hohlraum flux symmetry.