Pre-sales customer service is of importance to E-commerce platforms as it contributes to optimizing customers? buying process. To better serve users, we propose AliMe KG, a domain knowledge graph in E-commerce that captures user problems, points of interest (POI), item information and relations thereof. It helps to under stand user needs, answer pre-sales questions and generate explanation texts. We applied AliMe KG to several online business scenarios such as shopping guide, question answering over properties and selling point generation, and gained positive and beneficial business results. In the paper, we systematically introduce how we construct domain knowledge graph from free text, and demonstrate its business value with several applications. Our experience shows that min ing structured knowledge from free text in vertical domain is practicable, and can be of substantial value in industrial settings.