This article presents significant experimental data about the coaxial dual-pipe heat pipe which is new developed for applications of the heat pipe cooler in our CCT laboratory. It’s well known that heat pipe integrated with cooling plates has changed the heat transfer property of the heat pipe to be similar to copper pipe, where the heat transfer property of the bare heat pipe is discrete and the copper pipe is continuous. The integrated cooling plates cause the original heat transfer property of the heat pipe to be destroyed. For recovery of the original heat transfer property of the heat pipe in a heat pipe cooler, the coaxial dual-pipe heat pipe built a coaxial pipe inside the heat pipe in the thermal insulating section to avoid the heat of vapor being earlier taken away in the thermal insulating section. Experimental study in this work first built a home-made square coaxial dual-pipe heat pipe integrated with outside isothermal cycling cooling water. The home-made square coaxial dual-pipe heat pipe has an observation window and is convenient to observe the change of two-phase flow inside the heat pipe influenced by the outside cooling water. The results show that the new developed dual-pipe heat pipe cooler has kept the original heat transfer property of the bare heat pipe and therefore increases its cooling efficiency clearly.