The interconnection of distributed photovoltaic source（DPVS） may have adverse impacts on the traditional distribution network， such as over-voltages at the grid coupling point， so it is necessary to limit the on-grid peak capacity of DPVS. The maximum allowable capacity of DPVS under constraint of over-voltage is calculated with the yearly historical data. The over-voltage phenomenon is avoided by limiting the capacity of DPVS under maximum allowable figure. When the feeder is operating at a partial loading level， the allowed capacity of DPVS in the distribution network can be enhanced by operating DPVS with a leading power factor.