This study used high-fidelity conjugate heat transfer models to investigate the thermal-hydraulic performance of a micro-channel heat exchanger (MCHE) in a crossflow. The microchannel flow, solid domain, and crossflow were strongly coupled in the local flow field. The heat conduction in the solid structure produced a non-uniform temperature field with a higher temperature near the microchannel and a slightly lower temperature on the surface exposed to the crossflow. The impact on thermal-hydraulic parameters was investigated using computational fluid dynamics (CFD) simulation. The fin pitch impacts the temperature profile inside the microchannel. This study showed that the thermal efficiency and the performance index of the circular MCHE can be enhanced by decreasing the fin pitch within the same tube surface. The thermal effectiveness for MCHE with 0.06 in. and 0.08 in fin pitch are 0.561 and 0.467, respectively.