Larch (Larix principis-rupprechtii) plantation is one of the main forest types in Daqing Mountains of the Inner Mongolia, China. To investigate the response of carbon density increment of larch plantation to varying climate factors, five 30×30 m² plots were set up in 43 years larch plantation in Hadamen National Nature Reserve of Daqing Mountains of Inner Mongolia. Diameter at the breast height (DBH) of all trees in the five plots was measured, and forty tree-ring samples at breast height were got in each plot. Then, using dendroecological methods and biomass-DBH growth equations, biomass, carbon density and carbon density increment of larch plantation were calculated, and the relation between carbon density increment with climatic factors, including monthly precipitation, monthly temperature (monthly mean temperature, monthly mean minimum temperature, monthly mean maximum temperature), and monthly mean humidity was analyzed. The results indicated that the variation of carbon density followed the logistic equation as the increase of forest age, and the larch plantation carbon density increased from 1.05 t/hm² in 1979 to 76.83 t/hm² in 2016. The carbon density increment of larch plantation showed a trend of "slow-fast-slow" with the increasing forest age, with a mean carbon density increment value of 2.05 t hm^-2 a^-1 and a maximum carbon density increment value of 3.72 t hm^-2 a^-1. The carbon density increment was closely correlated with climatic factors. The carbon density increment of larch plantation was significantly and positively correlated with the monthly precipitation in June of previous year and that from June to August of current year, but negatively correlated with December in previous year. The carbon density increment of larch plantation was significantly and positively correlated with the temperature from November to December of the previous year and February, December of current year, but significantly and negatively correlated with humidity in those months. There was positive correlation between carbon density increment and the monthly temperature in July, September of the previous year and August-September of current year. In general, annual varying of carbon density increment of larch plantation was mainly affected by temperature, humidity and precipitation, which were primarily through influenced the growing season length, the relative extractable soil water in growing season and freezing injury and snow damage in winter. It is implied that the carbon density increment of larch plantations would present an increasing trend in the future due to the warmer and humidor climate condition in the research region.