Abstract: The application of MFE technique in formation tests is very common in the Tahe Oil Field; however, it is difficult to predict the formation pressure coefficient and fluid properties of exploratory wells. The chief by-pass valve of open hole is one-way sealed. It is easy to leak during well shutting when internal pressure is greater than external pressure. The assistant valve has a sleeve type structure. It might open accidentally when pressure changes due to fluid impact or perforation. As a result, oil tube and case are connected, and test fails. We replaced the chief by-pass valve by a two-way sealing valve, double the length of sealing core shaft sleeve, and remove the assistant valve. These measurements improve DTS success rate, and have been applied in field works in the Tahe Oil Field.