Abstract: Miniaturization of capillary pumped loop(CPL) is a developing trend in order to meet the requirement of heat dissipation of miniature high power-density electronic instruments.In this paper,a miniature CPL was experimentally investigated,with focus on the effect of attitudes on the operating characteristics of CPL in gravity and the thermal control characteristics at high heat flux.Based on the experimental results,the following conclusions can be drawn: the CPL can achieve successful startup at different attitudes,and present good thermal control performance during power step-increase tests.The CPL has a maximum heat transport capacity larger than 50W and a maximum heat flux higher than 12.5W/cm²,which can satisfy the requirement of heat dissipation of miniature high power-density electronic instruments.When the heat flux is low,the CPL can realize precise thermal control;however,when the heat flux is relatively high,the evaporator wall temperature fluctuates intensively,making it impossible to realize precise thermal control.