The invention discloses a preparation method of a dehydrogenation catalyst, which comprises the following steps of: loading a hydrogenation active metal group by adopting an immersion method and adopting an aluminum oxide carrier, then drying, carrying out water vapor dechlorinating on a dried material, and finally obtaining the dehydrogenation catalyst through thermal treatment, wherein the dechlorinating conditions of water vapor are as follows: the water vapor is treated for 1-20h at a temperature of 200-500 DEG C, and the hydrogenation atmosphere is nitrogen containing 10v percent-30v percent of water vapor. Compared with the prior art, the catalyst prepared by adopting the method has higher activity and selectivity, good stability and long service life when being used in a process for producing olefins by adopting light-alkane.