Abstract: Large grain niobium has good thermal conductivity at 2 K temperature because of the phonon peak, which is helpful to improve the thermal stability of superconducting cavities. The investigation into thermal conductivity and crystal imperfection of the large grain niobium material developed by Ningxia Orient Tantalum Industry Co., Ltd (OTIC) with different heat treatments has been carried out. Results show the phonon peak of OTIC large grain niobium can be recovered by heat treatment at a temperature of more than 800 ℃, which is different from previous measurements at DESY. In this paper we present the experiments, results and discussion of thermal conductivity investigation of OTIC large grain niobium.