Conventionally the intersection between horizontal well and vertical is processed by cavity building or hydropressurizing procedures, which consumes much construction time and costs. Nowadays, the newly developed ranging instrument “Smartmag” can accurately guide the drilling to the target well without need of the cavity building. With the case of well SY4 in Jiansu, the paper introduces “Smartmag” drilling guidance system of the independent intellectual property, which was used in a vertical well without cavity building. Due to the deviation data errors of the vertical wellbore, the drilling tool magnetization and the extremely small cavity, the intersection of the well pair is very difficult and finally achieved by 3 times’ ranging operations.