Abstract: The productivity formulas of branch horizontal wells which have or not have common joint are derived by applying conformal transformation and isopleth map of percolation resistance force. The paper gives a more detailed study on horizontal well productiyity and its influence factors such as the number of well bores, well length, formation thickness,formation anisotropy and horizontal well locations. The conclusion of the paper can be used to predict the productivity for a horizontal well with multi-branched boreholes in a practical reservoir development.