This study presents additional network planning using the tie-line method and the effect of improving bus voltage profiles on transmission systems taking into account the increased load during peak loads. The transmission system used is a transmission system in area Malang, with a transmission voltage is 150 kV - 70 kV. Malang transmission system has a semi-radial-type network, with load centered on a substation in the town area. Large load and critical voltage drop occur in bus KA and bus SKL included in area Malang, the voltage drop up to 6% of the base voltage. In this study, the author focus on the effect of adding a tie-line to the Malang transmission system for improving the voltage profile. To select the appropriate network addition, using methods based on areas that have a large load and a large voltage drop. The method used for this problem is Z bus, with Kron Reduction to reduce the Z bus value after the addition of the tie-line network. The addition of the tie-line network has an effect of the improvement voltage in Malang transmission system, also improves the stability of the voltage on each bus substation in Malang area. With the addition of the Tie-line, the benefits obtained are the decreasing of power losses that occur in the system, the voltage of each bus remains stable despite the addition of load power and the constant supply of the generator.