Abstract: Abstract: China is a large agricultural country and has considerable crop straw resources. Meanwhile, with the development of large-scale livestock farming, more and more wastes are produced, especially swine manure, which is the most significant, contributing 46.3 % of total livestock waste. From the perspective of utilisation,crop straw and livestock manure containing rich nutrient elements are useful organic matter resources. Utilising and recycling these organic resources are urgent issues bearing great theoretical and practical significance in guaranteeing the urban and rural environment and promoting regional economic development. Composting is an efficient way of agriculture waste disposal that can reduce pollutant amount, make the pollutant harmless and use it as a resource. However, the nitrogen loss during manure composting is relatively serious. Studies on this nitrogen loss and its control could provide theoretic basis and practical reference for efficient nitrogen loss control. In this study, static forced-aeration composting reactors were used to study the effects of two different additivesCa(H2PO4)2 +Mg(OH)2, H3PO4+Mg(OH)2 on reducing nitrogen loss of co-composting of fresh pig manure and corn straw.The changes of total nitrogen(TN)、ammonium nitrogen(NH4+-N)、nitrate nitrogen (NO3--N)content and ammonia(NH3) volatilization rate were measured during composting, as well as nitrogen fixation ratio in different phases was analyzed. The results showed that the additives not only reduced the amount of NH3 emission, but also postponed the maximum period of NH3 emission. Compared to the control, the treatments of Ca(H2PO4)2+Mg(OH)2 and H3PO4+Mg(OH)2 could reduce the amounts of NH3 emission by 41.78 % and 31.37 % respectively. The treatments of Ca(H2PO4)2+ Mg(OH)2 and H3PO4+Mg(OH)2 reduced the nitrogen losses as 28.63 % and 31.48 % respectively. Compared with the CK treatment, the nitrogen fixation rate of the correspondent treatment was 17.31 % and 5.57 % respectively. These results indicated that compared to the H3PO4+Mg(OH)2 treatment, the Ca(H2PO4)2+Mg(OH)2 treatment had the better effect of nitrogen loss controlling. Compared to the control, the NH4+-N and NO3--N contents of this treatment increased by 60.00 % and 24.66 % respectively at the end of the composting. The germination index of the end products were from 97.22 % to 115.86 %, which indicated that all treatments were matured after 35 days composting. The X-ray diffraction analysis confirmed the existence of struvite(MgNH4PO4·6H2O) in these treatments with additives.These results indicated that Ca(H2PO4)2+Mg(OH)2 and H3PO4+ Mg(OH)2 could accelerate the degradation of organic matter, and reduce the ammonia emission by struvite crystallization reaction. Moreover, because of the popular price and appropriate effect of nitrogen conservation,Ca(H2PO4)2 and Mg(OH)2 could be used as an additive in pig manure composting to reduce the ammonia emission and improve the value of compost as fertilizer.