Abstract: A complex well that display the characteristics of horizontal wells is an advanced well type and it effectively enhances single-well productivity and ultimate recovery in complicated oil and gas fields. The magnetic guidance drilling technique is one of the core techniques in complex well engineering. This paper presents the development of magnetic guidance drilling techniques, which involve the electromagnetic ranging tool for determining adjacent well distance while drilling, the electromagnetic ranging system based on a solenoid assembly while drilling, the ranging system based on three-electrode array for guiding a relief well to intersect a blowout well. This paper focuses on the introduction of technical principles, downhole magnetic beacons, downhole weak magnetic detectors, ranging algorithms, well trajectory control and other key techniques related to magnetic guidance drilling. The electromagnetic ranging system for the determination of adjacent well distance while drilling has been used successfully in the magnetic guidance drilling of twin horizontal SAGD wells for heavy oil development. It has been confirmed that the ranging system can be used to guide the well trajectory in directional drilling not only in horizontal sections but also in the building up sections. By strengthening coordinated researches involving multiple disciplines, the temperature-resistance performances of the magnetic guidance drilling systems can be further enhanced, and innovative high-temperature magnetic guidance drilling system can be developed. The application of magnetic guidance drilling techniques in complex wells can effectively enhance drilling efficiency and promote safety performances of such drilling operations.