Hu, T. Cao, L. Chen, Q.S. Chen, W. Li, J. Pei, Y.J. Qin, B. Tan, P. Tang, Zh. X. Xiong, Y.Q. WEP042 linac FEL target gun beam-diagnostic 2015 2015-12 The construction of a compact high-power THz source based on the free electron laser(FEL), which is constructed in HUST, is undergoing. Before the end of 2014, we have installed most of the key components, completed conditioning of the LINAC-based FEL injector, and performed first beam experiment. During last 5 months, we have established a high efficient beam diagnostic system with a reliable online monitor platform and precise data processing methods. At present, longitudinal properties such as the micro-pulse width and the energy spread are kept to a reasonable level, while transverse emittance compensation by adjusting focusing parameters is still undergoing. In this paper, we will give the summary on the commissioning schedule, detailed commissioning plan, the development of the commissioning and first performance of the LINAC, etc.