Abstract: The chaotic properties of the electromagnetic wave propagation in electrical, large complex cavities are analyzed by semi-classical approximation approach. The random plane wave hypothesis of three dimensional eigen-function is also induced. Based on this hypothesis and the random polarization of wave, the statistical approach to the solution of eigen-electromagnetic field spatial distribution problem establishes the statistical model. Importantly, those are independent of the details of cavity. Moreover, we numerically investigate statistical properties of three-dimensional Sinai microwave cavities, and numerical results are agreed well with those obtained from the statistical model.