The adsorption and complexation of organic polymer emulsion， acrylic emulsion （AE） was used to modify magnesium oxychloride cement （MOC）. The working properties， mechanical properties， water resistance and microstructure of modified MOC were systematically investigated， and the mechanism of the modification of MOC by AE was revealed. The results show that the dispersing effect of AE in MOC can increase the fluidity. AE formed membrane structures on the surface of cement particles and hydration products not only inhibit 5·1·8 phase crystals growth， but also change its morphology so as to influence the setting time and strength of MOC. Meanwhile， AE reduces the volume fraction of harmful pores of MOC. Combined with the membrane structure generated by AE inside the MOC， it can delay the hydrolysis of 5·1·8 phase crystals and reduce the generation of Mg（OH）₂ crystals. Thus， the water resistance of the MOC is improved.