Abstract: Aiming at the defects and internal damage of glass fibers in production process, a micro-magnetic detection method based on geomagnetic field environment was worked out. Firstly, the feasibility of micro-magnetic detection for glass fibers was analyzed. Glass fibers were tested by a laboratory-developed array magnetic flaw detector without any excitation in the geomagnetic environment. Comparing the test results with the actual defect position by cutting verification, the results show that the micro-magnetic detection method can effectively detect the holes in glass fibers, and the two-dimensional imaging of the detection results can exhibit the defects in the matrix in a graphical form, so that the determination of test results is more exact.