Scan forest can effectively compress test data volume, however, CPU time and memory consumption must be well-controlled to handle industrial designs. The present disclosure provides a method to establish a scan forest, which reduces memory consumption and CPU time significantly. A new low-power test application scheme is proposed, which does not need to increase the test application cost but can be of help to compress test data volume. Another new test application algorithm is proposed to reduce capture cycle power and shift cycle power by just doubling the test application time, which does not sacrifice the test data compression performance.