A simple expression for the yield strength of a thin polycrystalline film attached to a substrate and with a passivated layer has been derived from a relationship between stress work for dislocation moving and strain energy. It is shown that, the yield strength of a polycrystalline film is determined by two affecting factors (orientation of grains and type of dislocations) and three strengthening factors (passivated layer strengthening, substrate strengthening, and grainsize strengthening). Predictions from the expression are in agreement with reported experimental results. This shows that the model is reasonable.