Grinding materials as a pretreatment contribute to successful composting. Here the grinding ratio of 4 raw materials and compost samples with different maturity degrees were compared and discussed. Results revealed that the highest grinding ratio was obtained when drying the 3 straws into constant weight, but keeping water content around 10% for sewage sludge. The carbon-to-nitrogen ratio (C/N) was an important factor impacting the grinding ratio of raw materials except water content. Different straw materials had a decreased grinding ratio from the highest to the lowest in the following order: corn stover > rice straw > wheat straw. The grinding ratio of fermented compost significantly decreased lower than about 50% when the water content was higher than 30%, whereas no significant difference was observed when the water content was lower than 20%. Compared with original materials, mature compost had a better grinding ratio. Further regression analysis implies that grinding ratio had a negative linear orrelation with total organic carbon (TOC), C/N, hemicellulose, and cellulose, but no apparent correlation with pH, EC, GI, and lignin. Results reported here may provide an efficient way to save energy and investment in the industry production of pellet compost.