The solar radiation pressure on water cloud particles is analyzed with Mie scattering theory and the two stream radiative transfer method. It is found that this pressure can generally be some percents of the gravity on the particle whose radius is less than 10 μm, and that for a particle with radius about 0.3 μm, the pressure reaches the maximum and can be some tens percents of the gravity. Therefore the solar radiation pressure must be taken into consideration in the studies in cloud physics.