Abstract: A Ⅱb type diamond has semiconductivity and superconductivity as well as better heat resistance, wear and chemical inertia than a common synthetic diamond because of the doping of boron. In order to change the condition of high cost and hard to industrialization on Ⅱb type diamond synthesizing, this paper put forward a new synthesizing method using an Fe-Ni-C-B catalyst alloy made by powder metallurgy at high temperature and high pressure. Because of the presence of boron, a Ⅱb type diamond needs a higher temperature and pressure than a common Ⅰb type diamond. Due to the action of boron, the diamond has rough grain size, bad crystal shape and complex surface structure. The presence of boron was primarily ascertained by the color of crystal, X-ray diffraction and Raman spectrum. In addition, the thermal stability of the diamond was characterized with the results of static compressive strength and impact toughness at different temperatures, as well as DSC and TGA analyses. The experimental results show that the thermal stability of the Ⅱb type diamond is improved rapidly. Resistance-temperature characteristics measurement with a self-made clamp proved the semiconductivity of the diamond crystal. Based on summarization and analysis of experimental data, it is obvious that synthesizing a Ⅱb type diamond by this method can be realized easily with low producing cost and is available for synthetic diamond industry.