Abstract: This paper qualitatively analyzed influence of mining depth， coal-seam dip， mining height， mining face length， anti-broken ability and tectonic on water-conductive fissure zone under long-wall roof-caving mining. Applying gray correlation analysis method to quantitatively analyzing 31 data samples from all over the country， it showed that main controlling factors of water-conductive fissure zone in floor were mining face length and coal-seam dip.