Flow distribution and pressure drop in parallel micro-channels are two effective parameters on the performance of different devices. These two parameters are affected by different factors, such as the manifold geometry, channels geometry, flow rate and fluid direction of inlet flow. In the present work, the structure of the inlet manifold (the triangular geometry, with straight and curved walls) has been studied as the main subject. However, the effect of the flow rate (as the Reynolds number) and fluid direction of inlet flow has been studied on the flow distribution and pressure drop with these manifold geometries. The results show that in the low-Reynolds number range, with increasing the Reynolds number, the flow distribution does not change, but the pressure drop increases. Also, the vertical direction of the inlet flow in comparison with the horizontal direction is preferable. Flow distribution with triangular manifolds with curved walls is more uniform than with straight walls, while, in straight walls, equilateral triangle is a better choice. At the end of this consideration, the effect of geometry parameters (such as the channel number, channel width and depth of curvature) on the non-uniformity parameter was studied with concave manifolds.