As the nuclear magnetic resonance ( NMR) continues to develop towards the direction of portability and low cost, the miniaturization of the main magnet in the NMR has become a major concern. To realize the miniaturization of NMR, a low-field NMR main magnet based on Halbach structure is designed and implemented. Firstly, the ANSYS finite element simulation software is used to simulate the Halbach structure formed by the specific arrangement of multiple magnetic stripes to adjust the parameters, such as the number, size, length, and position of the magnetic stripes. Secondly, according to the ideal model parameters determined by the simulation, the main magnet, which is a cylinder of 108 mm diameter and 170 mm height weighing 4. 5 kg, is realized and its central magnetic induction strength and uniformity are tested. Finally, based on the test results, a uniform field sheet matrix is designed to improve the uniformity in the 5 mm diameter spherical region at the center of the magnet to 451. 68 ppm with a central magnetic induction of 221. 4 mT using passive uniformity. In the design, it is a good trade-off between magnet performance and production cost.