The relations between the precision of the transmittance turning point monitoring system and the thickness error of the monitored thin film layer are analyzed in this paper. The functions are derived under different conditions. This paper has developed a program to simulate the structures of deposited coatings and the real-time variation of the transmittance through the thin film stake and substrate assembly in deposition process that take the transmission turning point monitoring approach. The simulated value of the thickness of each layer after deposition is composed of the thickness correspond to the transmittance extreme found by 1D search algorithm and random thickness error calculated by the relations mentioned above. The computer simulation accord with the experiment results.
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