This article explores the microwave non-destructive testing technology for slit defects in medium to long distance pressure pipes. The characteristics of microwave transmission in bent pressure pipes and methods for slits detection were theoretically analyzed. The feasibility of detecting slit defects in straight and bent pipes was verified by simulating the transmission of microwave in medium to long distance pipes and the changes in microwave mode after passing through bend. Straight and bent pipes with a length of more than 5 m and a diameter of 8 cm were constructed and microwaves were introduced into the pipes using a vector network analyzer and a spiral antenna to detect axial, circumferential, and oblique slits, and the amplitude of the S11 parameter was varied in the case of slitless, slit, and even multiple slits to determine the location of the slits. For axial, circumferential, and oblique slits detection in straight pipes, the errors are 0. 047%, 0. 018%, and 0. 298% of the total pipes length, respectively. For axial, circumferential, and oblique slits detection in bent pipes, the errors are 0. 074%, 0. 065%, and 0. 203% of the total pipes length, respectively. This indicates that an effective remote detection method for medium to long distance pipes slits has been established.