The present work experimentally investigated the operating characteristics of a miniature loop heat pipe (LHP) under different power cycle. The miniature LHP with flat evaporator of 8mm thick is made of copper. The evaporator with sintered copper power wick is in series structure with compensation chamber. Water is working fluid. It is found that the LHP can start up at heat load of 15W with temperature oscillation and the maximum heat load is 160W with Rl=0.068°C/W. The LHP operates unstably under low heat load. The oscillating frequency of temperature rises with heat load increased. The operating performance of the LHP is affected by the power cycle.