Abstract Wedged and V-shaped cells have advantages on depressing strong absorption bands and keeping the photo windows wide open without absorption block. Alternatively, this work presents a concave cell design, which is constructed by a plano-convex CaF2 lens in combination with a flat plate. Mathematical equations have been provided for data treatment with Matlab programs. The result indicates that the concave cell has advantages similar to the V-shaped cell. Reflection-absorption measurements of ethanol have been conducted on the cell in mid-IR region for demonstration. The spectrum obtained from the concave cell can easily be interpreted to regenerate its normal spectrum, which is fitting well with the spectrum taken in a conventional thin-layer cell. The concave cell is easier to construct and more convenient to operate, willing to have popular usages.