With the increase of renewable energy penetration and various types of load demand, the 70 kV transmission lines are needed in power system of South Korea. In order to apply the new voltage level to the power system, its stability and reliability must be preferentially verified. The limitation on total capacity of all distributed generations (DGs) in the new voltage level can guarantee the stability of power system. This paper proposes an estimation method for the allowable capacity of DGs in the 70 kV transmission system and its sub-distribution system. First, reasonable technical requirements are established based on the protective coordination, short circuit capacity, and voltage stability. Then, the allowable capacities of DGs are estimated for new 70 kV transmission system and its sub-distribution system. As a result, the hosting capacities acquired by investigation of the protection coordination and the short-circuit current are 160 MVA for the test system with a single type of DGs. On the other hand, the various hosting capacities are derived by studying the voltage stability of test system.