Here we present an investigation of the variability of Venus' extended oxygen corona. For that, we employ a combination of a fluid model VTGCM for simulating Venus' ionosphere and thermosphere and kinetic model AMPS. We have found excellent agreement of the model results with PVO observations of the corona when the modeling is done assuming the solar maximum conditions, which corresponds to the solar conditions during the observations. We also found that the oxygen density strongly depends on the solar conditions and varies by order of magnitude over a solar cycle. That explains why the extended oxygen corona was observed only at the solar maximum. The result presented in this paper will be used in a later study of the planet's interaction with the ambient solar wind, where the corona model defines the mass loading coefficient.