Abstract: At present, the EFDT instrument with double-hanging probes for cable formation testing is the most widely used in Bohai Oilfield. It can simultaneously put the large plate probe and the conventional probe into the well, providing a variety of probe options for the sampling operation. How to make the sampling operation safe and efficient is a difficult problem in the selection of probes. Through the full research on the structure of the EFDT instrument with double-hanging probes, the selection range of the sampling probe is established. Combined with the sampling principle, influencing factors of the selection of probes are analyzed, and the suggestions on the probe optimization and operation points are put forward. The sampling efficiency of the EFDT instrument with double-hanging probes has been greatly improved, which provides a new idea for the cable sampling and the instrument development in Bohai Oilfield.