Beijing Astronomical Observatory, Chinese Academy of Sciences, Beijing 100080, China

Big Bear Solar Observatory, California Institute of Technology, Pasadena, CA 91125, USA

Based on the continuous observatin of vector magnetic field of NOAA 7469 from 4 to 12 April 1993, for the first time, the authors have identified the magnetic loop systems and relevant separatrices for such an active region. The observational signature ofthe cross-section of separatrices on the photosphere is as follows:

1. (1) High degree of magnetic shear at or close to the separatrices;

2. (2) Steep gradient of line-of-sight magnetic field ( 0.1 G/km) crossing the neutral line.

3. (3) Flux cancellation from both sides of the separatrices. At this point the transverse field partly changes its alignment.

During the observed period, flare activity took place repeatedly in the vicinity of the separatrices.