Abstract: Classically, the Klein-Gordon equation was treated as the equation of boson. However, we argue that Klein-Gordon equation is the equation all microscopic particles obey, but not the wave equation for any sorts of particles. We propose that the Klein-Gordon equation contains probability wave and non-probability wave. The probability wave must obey an equation in which the first-order derivative to both time parameter and space parameter appear. We refer to this equation as the wave equation of particles. The different properties of particles root in their different probability wave.

Key words: probability wave, non-probability wave, two-component spinor, four-component spinor, three-dimensional vector, four-dimensional vector