In order to prolong the service life of reduction jar and reduce the production cost in the magnesium metallurgical industry, the structure of the horizontal Mg-reduction jar is improved in this paper, where the reduction jars with pentagonal and hexagonal cross section are designed, and the creep deformation of the jars are simulated by ABAQUS software. Through the comparison of the traditional jar with the improved jars in the creep stress and the creep displacement, it is found that the intensity is highest and the creep displacement smallest in the same service period for the pentagon jar. Considering the failure by creep, the service life of pentagon jar is longest. Therefore, the pentagon jar is put into the practical production for further verification. It is shown that the service life of the jar improves from less than 90 days up to more than 120 days, and the rate of output for a single jar is stable and improved by 12%.