To apply the composite material of magnesium oxychloride cement (MOC) doped with paper mill sludge (PMS) to engineering, the four modifiers such as phenylacrylic emulsion (PE), sodium methyl silicate (SMS), sodium phosphate monobasic (SPM), and citric acid (CA) were used to explore their effects on the composite material. The effects of these modifiers on the setting time, flowability, mechanical strength, softening coefficient, and strength loss coefficient of the composites were analyzed by physical properties, mechanical strength, water resistance, and resistance to sulfate attack, as well as by XRD. Results show that all four different modifiers can delay the setting time of the slurry and increase the fluidity of the mortar. With the increase of modifier dosage, the strength of mortar modified by different modifiers is lower than that of the control group, and the softening coefficient and sulfate erosion resistance coefficient of the modified mortar are significantly improved. At 2% and 1.5%, respectively, SPM and CA have the best modification effects, but PE integration decreases the softening coefficient of the mortar and only increases it by 47.30% at 0.5%. The obtained conclusions can provide a reference for the engineering application of PMS-MOC. Keywords: Magnesium oxychloride cement, Paper mill sludge, Composite materials, Modification, Softening coefficient.