In order to select suitable lines and reduce approval process effectively, the article presents a method to evaluate access capacity based on total supply capability. Firstly, after making a brief introduction to total supply capability, we define access capacity and give two access capacity indexes, which are substation supply access capacity and network transfer access capacity. Secondly, based on constrained information of substation supply capability、network transfer capability、node voltage and node current, we present a model to evaluate access capacity and calculate it. At last, based on this method the article evaluate access capacity of a distribution network line with 44 nodes, the results show that this method can reflect the access capacity in distribution network line accurately.