Loop heat pipes (LHPs) have a great potential for applications of electronic cooling due to the advantages of high transfer capacity, low thermal resistance and long transport distances. However, the cylindrical evaporators of loop heat pipes cannot work on a flat thermo-contact surface without saddle. The saddle not only creates an extra thermal resistance but also makes evaporators less isothermal. To avoid the above disadvantages, we adopt the flat evaporators of loop heat pipes. According to the literatures, however, the heat leak problem is more serious in the flat evaporators than the cylindrical evaporators. This problem makes the thermal resistance of flat evaporators higher. Hence this study tries to solve the difficulties and provides two solutions. The first method is to increase the thermal resistance of the wick by raising the wick thickness. The second method, we design a double-decked complex wick, which is composed of the main wick sintered with metal powder and the additional wick made of the low thermal conductivity polymer. The material wick generates higher capillary forces and the polymer has lower thermal conductivity. Such designs can ease the heat leak problem. The results showed that both methods can ease heat leak problem. When the temperature of the evaporators was less than 100°C and the sink temperature was at 30°C. The maximum heat capacity reached 180W with thermal resistance 0.38 K/W ,and the heat flux is 14.32W/cm2.