A systematic research on ultra-low field magnetic resonance imaging (MRI) is conducted based on high-Tc dc-SQUID senor. The coil system is first updated to reach the requirements of MRI experiment. After that one-dimensional and two-dimensional imaging are performed and images consistent well with original phantoms are obtained successfully. Two different methods are used to rebuild the image: direct back projection and Fourier transform reconstruction. Both of them can obtain the profile of water phantom. A comparative discussion between these methods is proposed: the Fourier transform method has a better profile, while the direct back projection has a better signal-to-noise ratio. Imaging of biological sample such as green pepper and celery is also performed, and it is consistent well with the physical object.