The composition and evolution characteristics of inorganic anions, ammonia, heavy metals and organic compounds in leachates with different composing times were studied in a composting plant in order to clarify its composition and evolution and search for a suitable processing technology. The results showed that concentrations of EC, F-, Cl-, SO4(2-) and NH4(+) -N decreased during the composting process, while the contents of NO2(-) -N, NO3(-) -N and Org-N were related to the oxidation reduction atmosphere of leachates. The Pb, Cd, Cu, Zn and As concentrations in leachates exhibited a decrease trend during the composting process, while contents of heavy metals Cr, Ni, Fe, Mn showed an increase trend with increasing composting time. The composting leachate organics comprised mainly of protein-like substance, but also consisted of humic-like substances. The leachate organics were suitable to be treated by biochemical process firstly, and then by physico-chemical technique. The relative content of protein-like substances firstly increased and then decreased, while that of humic-like matter exhibited an opposite trend. The contents of salinity and heavy metal in compost leachates were high, which caused the improper reflux utilization of leachates. The compost leachates should be treated by the combined biochemical and physico-chemical process before emission.