An open cluster is an ideal region to study the evolution of stars. In this work, we use Gaia Early Data Release 3 (Gaia EDR3) to derive the fundamental parameters of 30 faint open clusters listed in the catalogue given by Cantat-Gaudin et al. (2018, A&A, 618, A93), but the G magnitude of all of the member stars of that catalogue is brighter than similar to 18 mag. This catalogue does not provide isochrone fitting parameters and spatial structure parameters. We acquired the member stars of 30 open clusters using the Density-Based Spatial Clustering of Applications with Noise algorithm in Gaia EDR3. The G magnitude of the member stars using our method can be found down to similar to 21 mag. The G-band, G(BP) - band, and G(RP)-band data of the member stars construct a good color-magnitude diagram, which can further ensure the precision of isochrone fitting. We also calculated the spatial structure parameters, which are the core radius and the limiting radius, using Markov chain Monte Carlo algorithm.