SOC technology has developed rapidly

which makes the test data of SOC increasing dramatically.This paper presents an effective test data compression algorithm

Variable-Run-Length code.Both runs of 0s and runs of 1s in test data stream are mapped to codeword so as to reduce the number of short runs and improve compression radio.Theoretical analysis and experimental results show that Variable-Run-Length code can provide a higher compression radio than other compression algorithms and it also leads to a significant saving in peak and average power due to a careful mapping of the don't-cares in precomputed test sets to 1’s and 0’s.