This paper investigates the heat transfer performance and characteristics of liquid cooling heatsink containing microchannels. The porosity analysis is utilized to study the thermal resistance of the heatsink with microchannels. Both numerical simulation and experimental work have been carried out. Results show that the effective thermal resistance of the heatsink was affected by both channel aspect ration and the pressure gradient. It is found that channel aspect ratio of 8 present the lowest effective thermal resistance at low pressure gradients. However, the lowest effective thermal resistance appears for channel aspect ratio of 11 under high pressure gradients. As an overall inspection, the value of the effevtive thermal resistance ranges from 0.32 to 0.65°C/W with various porosity at low pressure gradients, while it ranges from 0.18 to 0.37°C /W at high pressure gradients.