In order to improve the reliability of distribution power supply, the tie-line planning is optimized to form its owner ring for a single power source tree distribution network. The tie lines connection position impacts load transfer, which is analyzed by the node and node unicom matrix, and then outage cost calculation method is put forward based on the affiliation of fault section relative to the tie lines. The mathematician model of tie lines planning is founded, in which the weight sum of outage cost and construction cost is regarded as the objective function, and with a constraint to adapt to the different operation modes of protection setting values. The optimization of the tie lines can be regarded as a multistage decision problem and solved by using dynamic programming principle. The locations of the tie lines are chosen for the state of the dynamic programming, and the number of the tie lines is chosen for the number of dynamic planning stage. The results show the effectiveness of the algorithm by analysis of the IEEE33 node system example and field-oil engineering example, and in which the economic indicators, such as the construction cost and outage cost etc. are compared. This work is supported by Natural Science Foundation of Shandong Province (No. ZR2012EEL20).