In this paper, a new type alkoxy silane plasticizer is synthesized with organosilicon high-boiling component and octanol. The effect of reaction temperature, reaction time and molar ratio on the synthesis were studied，and the proper technological conditions were obtained. The optimum reaction conditions were: mole ratio of chlorosilane to octanol is 1:6,reaction time is 21h at 110℃. Under the optimum conditions, the content of organic chlorides can be as low as 3.02%. Experimental results indicated that when the content is 10%, this plasticizer could improve the performance of the silicone sealant greatly. In addition, the application of this plasticizer could solve the oil leaking pollution problem to the building. Keywords: building silicone sealant; plasticizer; oil leaking pollution.