Based on complex goaf and hydrologic condition of mining area, caving zone and water flowing fractured zone were calculated by experience formula method and times of coal thickness method respectively. The result showed that experience formula method was only applicable to 1-3m single layer thickness, 20 times coal thickness method computation was used to water flowing fractured zone when seam thickness was more than 3m and maximum height was 114.80m. These methods provided data support and empirical calculation to reasonable evaluation on effect of coal mining in goaf under similar geological conditions.