With the extensive application of the SmartMag system in various fields, the requirement on the precision of target-hitting is getting higher. How to enhance the measurement precision of SmartMag to realize ultra-high precision target-hitting is a problem that must be solved during horizontal well intersection. In the paper, analysis of the factors that may affect the measurement precision is conducted, including the tool face of the mud motor, magnetic environment of the measurement, vibration of the probe, and position of the probe in the borehole; and the solutions are provided accordingly. Then, a series of field tests were conducted at surface for horizontal well intersection, and the results showed that the measurement precision of SmartMag is significantly improved and ultra-high precision target-hitting is realized. The test results in the paper can be used as reference for improvement of the trajectory control for horizontal well intersection and the one-time success rate of target-hitting where the target cavity size is limited or undeveloped.