The inverter drive system stability is a classical problem but not understood widely and fully by the industry. Especially for railway traction applications with substations and network distributed parameters also taken into consideration, the question becomes very complicated and so far, there is no satisfactory analytical method or model to cover the whole system in the literature. This paper firstly used the root-locus method to study system parameters' influence on the drive stability. It then used Routh-Hurwitz method and small disturbance method to study the typical drive system stability. As the result, a more comprehensive tool for inverter drive stability calculation is developed which is based on the Matlab platform.