Abstract: Outside annular chemical packer (ACP) for horizontal wells is determined to be used to enhance the development efficiency of horizontal wells and solve the technique problems such as water hinting, water controlling and water plugging in this kind of wells. Based on the key technique problems of thixotropy, outside filling shape stability and plugging strength of ACP materials, a new type outside ACP material XAN-SP has been studied. The thixotropy, gel strength and filled shape stability for the new slurry have been analyzed by compressive strength, liquidity and shear strength tests. The plugging strength and expansion property of XAN-SP were evaluated during the process of XAN-RC plugging stimulated experiment; three stimulated tests flows were designed to imitate ACP applied in field case, and then the technique parameters of ACP for site operation were obtained. The experimental results showed that XAN-SP is an advanced ACP material characterized by well thixotropy, stable filled shape and high plugging strength; besides, the final site practice indicated that ACP treating parameters determined by stimulated test could guarantee the field operation treated smoothly and safely.