Abstract　 　　
　 Solar eruptions, i.e., solar flares, filament/prominence eruptions, and coronal mass ejections (CMEs) are different manifestations of the same physical process, i.e., the release of magnetic free energy stored in the corona. At first, I will present preliminary results on the investigation of one polar crown prominence that erupted on 2012 March 12. This prominence is viewed at the east limb by SDO/AIA and displays a simple vertical-thread structure. Bright U-shape (horn-like) structure is observed surrounding the upper portion of the prominence before the eruption and becomes more prominent during the eruption. When viewed on the disk, STEREO-B shows that this prominence is composed of series of vertical threads and displays a loop-like structure during the eruption. We focus on the magnetic support of the prominence by studying the structure and dynamics before and during the eruption using observations from SDO, Hinode, and STEREO. We will also present preliminary analysis on the thermodynamics of the prominence, namely DEM analysis of the cavity surrounding the prominence, as well as column density measurements. For the second part of my talk, I will present observations and NLFFF modeling of an X2.1 flare occurred on 2011 Sep 6. The multi-ribbon structure can be explained with the fan-spine topology as derived from the NLFFF model. We find that the axial flux in the best-fit pre-flare model is close to the threshold instability which suggests the flare may be triggered by loss of equilibrium due to build up of axial flux driven by shear motion. The magnetic free energy in the best-fit pre-flare model is much smaller than that expected energy release during X flares, indicating an underestimation of the free energy in the model. We also find that the measured magnetic field strength is about 286 G near the flaring reconnection site.