During the international campaign of June 1991, the active region AR 6659 produced 6 very large long duration flares at the same location during its passage across the solar disk. Vector magnetograms were obtained at Marshall (Huntsville) and Huairou Station (Beijing) with a time difference of 10 to 12 hours, thus giving a good survey of the magnetic field evolution with time. The flare of June 6/01:08 UT (X12 plus/4B) was observed in Shahe Station (Beijing) in white light, in Hα and in radio centimetric wavelengths. The evolution of the flare of June 9/01:43 UT (X10/3B) has been followed in Hα at the Yunnan Observatory (Kunming). An other one was well observed on June 15 at 08:20 UT in Wroclaw and in Debrecen. Some subflares were observed at Sac Peak on June 4, 5, 7 at Meudon on June 10, 14 and Debrecen on June 12 and 13. In this short communication we concentrate on the relationship between magnetic field shear and flare sites.