Vietnam today, hydropower still make a large proportion and power supplies primarily, especially in the peak hours. The development of hydropower formed stairs hydropower system on the river basin. In stairs hydropower system, there are upper stairs hydropower system not to be submerged in the water level of under reservoir, or there are hydropower systems on the water level of the under stairs reservoir. This article, author present how to determine the appropriate altitude of hydropower plants in stairs hydropower system, applied to Pa Chien hydropower plants. This is a reference document to calculate, design for the same hydropower plants.