At the Plasma Research Center (PRC) in University of Tsukuba, development of Mega-Watt Gyrotrons is performed for fusion research. Development of a new 154 GHz 1 MW gyrotron for ECRH system of Large Helical Device (LHD) has been done. The design studies of electron gun (MIG), cavity oscillator, mode converter, transmission mirrors, collector and superconducting magnet (SCM) have indicated more than 1 MW output with efficiency ~33 % for cavity oscillation mode of TE28,8. In the short pulse test of the first test tube, the maximum output power of 1.06 MW and the maximum total efficiency of 35.2 % with CPD were obtained.