Abstract: Abstract: This paper was aimed to investigate the effects of organic fertilizer application (single application of organic fertilizer and organic-inorganic fertilizer combination) on the CO2 emission in farmland soil during crop growth period, under different climate types, fertilization measures, organic fertilizer types and experiment years in Northern China. Non-fertilizer and inorganic fertilizer application were used as control treatments. Based on the published data of relevant experiment and the Meta-analysis method, the quantitative effects on application of organic fertilizer and organic-inorganic fertilizer combination on CO2 emission in farmland soil were studied. A total of 534 measurements were obtained including 89 pairs of data from 21 literatures. The experiments lasted from 1980 to 2017. The effects were determined by effect size by Meta-analysis method. The important factors affecting CO2 emission were selected by finding out those with important values higher than 0.8. The results showed that the organic fertilizer application significantly generally increased the CO2 emission in farmland soil than the non-fertilizer and inorganic fertilizer application, with an increment of 50.6% and 36.3%, respectively. No publication bias was found because the fail-safe number was far higher than the critical values by the fail-safe method. There was not significantly different among regions (P>0.05). Under the application of organic fertilizer, the CO2 emission of farmland soil decreased successively in the following order: single application of organic fertilizer, organic-inorganic fertilizer combination, and combined application of inorganic fertilizer, organic fertilizer and slow-release fertilizer. Soil CO2 emission did not significantly increase under the combined application of organic fertilizer, inorganic fertilizer and slow-release fertilizer. Compared with non-fertilizer, cow manure, pig manure and commercial organic manure, chicken manure had the greatest positive effects on soil CO2 emission. Under the application of organic fertilizer, the CO2 emission of farmland soil in gray desert was relatively high. The CO2 emission of farmland soil was positively correlated with the annual average temperature and negatively correlated with the annual average precipitation. The annual average temperature and annual average precipitation could explain about 11%-16% and 10%-12% change in effect size of CO2 emission, respectively. From the perspective of environment, it was suggested to apply the combined application of inorganic fertilizer, organic fertilizer and slow-release fertilizer in Northern China. Meanwhile, the chicken manure should not be applied in large quantities and organic fertilizer should not be used in grey desert farmland. The results of this study can provide valuable information for the popularization and application of organic fertilizer replacing partial chemical fertilizer in Northern China.