Tester valve is used with safety sealing and open hole packer, which is suitable for open hole well testing. The tester valve is controlled by drilling string’s vertical motion, the main parts: main by-pass, secondary by-pass and metering valve. It can make mud go through the by-pass hole on packer’s upper part when descent down hole and encounter tight hole section during ascent. While applying drilling string weight, it can close quickly to release drilling string’s pressure, and the by-pass valve will open after being applied 88.9 KN (20000Psi) pulling power(bigger than free point) for 1-2 minutes delay, also can open by super addition pulling power instead of time delay. Open tester valve after testing can balance the pressure on upper and lower part of packer. It can provide safety insurance for the closing and opening of tester valve if open the time delay function of by-pass valve. Hydraulic oil can flow through the interspace between valve mandrel and valve during descent down period, with the result that the main by-pass hole will be closed while going through tight hole section if must by using crown drill, so we need equip a secondary by-pass under any condition in order to let mud through when descent down hole.