Abstract: During pump inspection, the fluid from oil well often blows out and pollutes the environment, to solve this problem and at the same time to meet the needs that the immovable string passing through annulus for testing during production, the research on the blowout prevention technology of the well that can be tested in the annulus was carried out. The core tools such as Y445 packer and spool type downhole switch were developed, and these core tools together with oil well pump and poke rod formed a set of blowout prevention pipe string. During production, the spool type downhole switch will be in an open state, with a minimum inner diameter of Ø36 mm, which provides a central channel for the testing instrument to be lifted and lowered. While during pump inspection, the lowered pump string will close the spool type downhole switch to prevent well blowout. The sealing and anchoring performance of the process pipe string under different casing pressures from 0 to 25 MPa was analyzed by finite element simulation. The simulated results show that the blowout prevention pressure is 28.4 MPa, and the anti-jacking force is greater than 422 kN. The laboratory test results show that the process string is safe and reliable under the casing pressure of 25 MPa. The technology has been tested on 5 wells in Daqing Oilfield, including 2 wells for secondary pump inspection. There is no overflow at the wellhead during the whole testing process, and the testing instrument passing through annulus producing profile passes smoothly and without jamming. This technology has successfully realized the pump inspection operation without killing well and the testing passing annulus without moving pipe string.