Pulse cascades are non-conventional and may suit the flexible demand for stable isotopes varying in varieties and quantities. The separation power in pulse cascades is evaluated, and the definitions and the expressions of the separation efficiency are given respectively. They are both analyzed and studied, and are found having close relations with the pipe holdup and the pulse period. It is better to adopt an appropriate pulse period and a proper pipe holdup for a pulse cascade to obtain a large degree of separation and high separation powers and separation efficiencies in a short transient time.