In this paper ,firstly ,by comparing the propagation of light to the mechanical motion of a body, it is pointed out that the propagation of light is not a mechanical motion, the speed of light is not a velocity of mechanical motion and the Galilean relativity principle of mechanics is extended to optics lacks any evidences of theory and reality; secondly, from optics, there is no irreconcilable conflict between the principle of constancy of light velocity and Galilean coordinate transformation, in the special theory of relativity it is thought that the principle of constancy of light velocity contradicts the Galilean coordinate transformation because the propagation of light is looked upon as a mechanical motion and the speed of light looked upon as a velocity of mechanical motion; thirdly, the scientific theory has a range of validity, the range of validity of mechanics is the mechanical motion of a body, the range of validity of optics is the propagation of light; fourthly, the scientific and rational explanation to the Michelson-Morley experiment is to apply classical optics, it is called the speed of the earth relative to the ether is zero, which is not that classical physics has problems, but it is wrong that some physicists look upon the propagation of light as the propagation of light wave occurred in the ether to explain the Michelson-Morley experiment; fifthly, the real and natural space stays the same with the change of the frame of reference; sixthly, the property of time and space of the special theory of relativity is not consistent with reality; seventhly, the present experiment can not confirm the special theory of relativity sufficiently.