1. A corpus expansion system, comprising: a corpus collection unit, for collecting corpus using sample seeds; a sample seed expansion unit, for generating new sample seeds, based on the sample seeds having been used by the corpus collection unit and the collected corpora; a balancing unit, for determining a corpus expansion strategy based on all the sample seeds having been used by the corpus collection unit and the new sample seeds; and a refining unit, for refining the new sample seeds based on the corpus expansion strategy.