The invention provides a line loss intelligent evaluation and assistant decision-making system for a distribution network. The system comprises a data collection subsystem, a standard dictionary database subsystem, a power grid model management subsystem, a distribution network line loss computation subsystem and a line loss simulated analysis subsystem. The standard dictionary database subsystem is used for setting voltage class information, line type information and distribution transforming type information of the distribution network. The power grid model management subsystem is used for setting factory stand information, feeder line information and region information needed for simulating calculation of the distribution network. According to the set distribution network information, a power grid model is designed, various kinds of power equipment is drawn, and equipment parameters or states are set. The distribution network line loss computation subsystem carries out accurate load flow iteration computation by utilizing the power grid model, a power grid loss module, an electric energy collection system and data of an electricity meter reading system to obtain a theoretical line loss. The line loss simulated analysis subsystem carries out comparison on actual line losses, analyzes management line losses, analyzes composition of the line losses of the power distribution network and occupied proportions of various losses, and establishes a line loss analysis report. Optimization is carried out according to all computed line loss weights, and powerful supporting is provided for loss reduction decision making.