The invention discloses a process for preparing manganese chloride tetrahydrate by absorbing waste gas containing chlorine by low-taste rhodochrosite. Powder of the low-taste rhodochrosite is prepared to be ore pulp with water; the ore pulp carries out absorption reaction with the waste gas containing the chlorine; the obtained ore pulp is carried out filtration; manganese sulfate powder and metal manganese powder are sequentially added in the filtrate to carry out the purification and the filtration; after the filtrate is evaporated and crystallized, solid MnCl2 4H2O product is obtained. Compared with the prior art, the invention has simple technological process and is convenient to operate. The invention solves the problem of treating the waste gas containing the chlorine, makes full use of the oxidizability without adding oxidant and can also highly effectively use a large amount of low-taste rhodochrosite resource which is difficult to use, which realizes sustainable utilization of resources and reutilization of secondary resources and has good application prospect in industry. By adopting ways of displacement of the metal manganese powder and reduction of the manganese sulfate when purifying and eliminating heavy metals, the invention not only has obvious effect but also reduces secondary pollution to the product and saves process of secondary impurity removal.