In this study, phase diagrams of form II (metastable form) of pyraclostrobin under different cooling rates were measured with the aid of in situ tools such as ATR-FTIR, FBRM, and PVM. It was found that the initial concentration of pyraclostrobin corresponding to the metastable state critical oiling out point upon cooling decreaies with the increase of cooling rate. Meanwhile, the seeding strategy experiments illuminated that seed loading and seed size are important factors to avoid the oiling out and to obtain form IV (stable form) of pyraclostrobin. By optimizing the cooling rate and employing the seeding strategy, oiling out could be eliminated and products of pure form IV of pyraclostrobin could be obtained.