A new scheme of test data compression, namely equal-run-length coding (ERLC) scheme is presented,which is based on run-length. It first considers both types of runs ofO's and's, then itfurther explores the relationship between two consecutive runs on the basis of the traditional characteristic of run coding which uses shorter codeword to represent longer symbol (runlength). This scheme uses two shorter codewords to represent the whole second run of two consecutive runs,the lengths of which are the same. Compared with other already known schemes this scheme has some characteristics, such as high compression ratio, easy control and implementation. The performance of the algorithm is mathematically analyzed and its merits are experimentally confirmed on the larger examples of the ISCAS89 benchmark circuits.