It is analysed the discrepancy about the coronal magnetic field between solar optic and solar radio using magnetic fibril concept with filling factor and fractal structure model. The magnetic field of ~ 100 G considered in solar optics is mean value in a large scale, and that of ~1000 G in solar should be the value of fine structures inside 'macro' loop.

It. has been discovered that. active regions commonly have numerous flare-like transient. loop brightenings. We use a magnetic reconnection theory driven by a ponderamotive force on account. of the basic properties of a transient. brightening: lifetime a few mins, total energy 10 25~10 29 erg. The numerical results are consistent with the observations.