The idea of parallel prose(pianwen) as practical writing was so highlighted that it became the fundamental understanding in the Song Dynasty. Consequently, the separation between practical writing and others became clear, so that the former adopt the parallel style while the latter the free style. The evaluation of "practical" parallel prose was diversified, some considering it as useful while others useless. Only focusing on the idea of parallel prose as "practical" writing can we deepen the research of parallel prose in the Song Dynasty since the word "practical" was essential to the understanding and evaluation of parallel prose in the Song Dynasty.