Using high spatial and temporal data from the Solar Dynamics Observatory (SDO) and the Interface Region Imaging Spectrograph (IRIS), several observational signatures of magnetic reconnection in the course of magnetic flux cancellation are presented, including two loop-loop interaction processes, multiple plasma blob ejections, and a sheet-like structure that appeared above the flux cancellation sites with a Y-shaped and an inverted Y-shaped end. The IRIS. 1400 A observations show that the plasma blobs were ejected from the tip of the Y-shaped ends of the sheet-like structure. Obvious photospheric magnetic flux cancellation occurred after the first loop-loop interaction and continued until the end of the observation. Complemented by the nonlinear force-free field extrapolation, we found that two sets of magnetic field lines, which revealed an X-shaped configuration, aligned well with the interacted coronal loops. Moreover, a magnetic null point was found to be situated at about 0.9 Mm height, which was right above the flux cancellation sites and located between the two sets of magnetic field lines. These results suggest that the flux cancellation might be a result of the submergence of magnetic field lines following a magnetic reconnection that occurs in the lower atmosphere of the Sun, and the ejected plasma blobs should be plasmoids created in the sheet-like structure due to the tearing-mode instability. This observation reveals a detailed magnetic field structure and a dynamic process above the flux cancellation sites and will help us to understand magnetic reconnection in the lower atmosphere of the Sun.