According to the principle that the oxidation chemical reaction between metal calcium film and water vapor makes calcium film transparent, this experiment measures the corrosion area of calcium film to characterize the quality of water vapor passing through high barrier plastic film, so as to measure the water vapor transmission rate of high barrier plastic film. The effects of corrosion time, thickness of calcium film and barrier property of samples on the determination of water vapor permeability were analyzed with vacuum evaporation calcium film as pretreatment method and regular monitoring of calcium corrosion area as detection method. The results show that at 40 ℃ and 90% RH, the high barrier and ultra-high barrier plastic films with a thickness of 200 nm and a nominal water vapor permeability of 10^-6~10^-3 g/(m²·24 h) at the initial stage of calcium corrosion show a good linear relationship between the calcium corrosion area and the water vapor permeability. The water vapor permeability is 1.2×10^-3 g/(m²·24 h) and 9.3×10^-7 g/(m²·24 h), respectively, with RSD of 11.6% and 16.5%. The results of water vapor transmission of high barrier and ultra-high barrier plastic films by calcium etching method are good, and this method has a high application prospect in the measurement of water vapor transmission of high barrier and ultra-high barrier packaging materials in electronic components, solar cells and organic light emitting diodes.