The degradation of simulated methyl red dye wastewater in a concentric tubular reactor using dielectric barrier discharge low-temperature plasma technology was studied. The effects of discharge power, initial solution concentration, initial pH, treatment time, and atmospheric conditions on the degradation efficiency were studied. The color, pH, and absorbance of methyl red at 521 nm were used to detect the dye concentration, analyze the degradation process, and propose a degradation mechanism for methyl red. The results indicate that (1) in this experiment, the discharge power affects the degradation of methyl red but is limited by temperature and humidity, such that there is no positive correlation between the discharge power and the treatment effect. Therefore, the treatment of the solution at a low discharge power of 115 W is preferable; (2) the higher the initial concentration, the longer the time needed to achieve the same degradation rate as that achieved at lower concentrations; and (3) under the same conditions, a low pH is conducive to the degradation of methyl red, and acidic conditions are conducive to the bond breaking of methyl red.