We investigate the fluctuating domain walls in Co nanofilms during Barkhausen avalanche from direct time-resolved observation of magnetic domains. By statistical analysis of repeated observations of domain wall configuration, we generate the probability map of finding domain wall at a certain position. Interestingly enough, there clearly exists a more probable region where domain wall prefers to be pinned but still with fluctuation. Our direct and quantitative analysis enables us to determine the degree of reproducibility in avalanche with microscopic details. (C) 2003 Elsevier B.V. All rights reserved.