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We study the oxygen reduction reaction (ORR) mechanism on the square paddle-wheel cage active site of TM-BTC (TM= Mn, Fe, Cu) metal organic framework by using a combination of DFT and microkinetic calculations. By using a small cluster for modeling the TM-BTC active site structure, we have successfully reproduced the experimental trend of ORR activity on the TM-BTC systems: Mn-BTC > Fe-BTC > Cu-BTC. We also show that the unusual ORR activity trend from experiments for Mn and Fe systems is originated from the strength of OH adsorption on these systems. Mn-BTC system has better ORR activity than the Fe-BTC system because it has weaker OH adsorption. A very strong OH adsorption makes the final OH reduction step become more sluggish, and hence hindering the ORR process.