The invention provides a cavity surface preparation method of a semiconductor laser and a cavity surface preparation device thereof. The method comprises the following steps: placing a wafer strip with a cleavage line into a cleavage cavity, and cleaving by the cleavage cavity according to the cleavage line to obtain at least one bar; transmitting the at least one bar to a passivation cavity, so as to passivate two cavity surfaces of each bar; and transmitting the at least one bar to a coating cavity, evaporating a high reflective film and a high transparent film on the two cavity surfaces of each bar respectively, and finishing the cavity surface preparation of the semiconductor laser, wherein the cleavage cavity, the cleavage cavity and the coating cavity are all in the vacuum state. The cavity surface preparation method of the semiconductor laser provided by the invention cleaves and passivates the semiconductor laser in the vacuum state, and directly evaporates optical films of front and rear cavity surfaces of the semiconductor laser in a vacuum, which can effectively avoid the optical films from being contacted with air, avoid the contamination of the cavity surfaces by impurities such as oxygen and carbon in air, and avoid the formation of a surface state on the cavity surfaces, so as to effectively suppress the generation of catastrophic optical damage of the cavity surfaces.