Agricultural machinery has increasingly become an important source of air pollution in China, and its emission problems need more in-depth research. To investigate the effects of burning different proportions of biodiesel in agricultural tractors at high altitudes on the emission characteristics of CO (carbon monoxide), HC (hydrocarbon), NOX (nitrogen oxides), and PN (particulate number) under the actual operating conditions, the study compared and analyzed the effects of blending B10 (10% by volume of soya bean methyl ester biodiesel + 90% by volume of diesel fuel), B20, B30 and diesel fuel (B0) in a National III emission standard agricultural tractor at an altitude of 2200 m. The study was carried out in the same way as that of the national standard agricultural machinery. B10 (10% by volume soybean methyl ester biodiesel + 90% by volume diesel fuel), B20, B30, and diesel fuel (B0) at 2200m above sea level during rotary plowing (with the engine speed at 1500 r/min to 1700 r/min and the engine power at 20kW to 30kW). OBD (board diagnostics) and PEMS (portable emission measurement system) were used to collect data on tractor operating conditions and pollutants, respectively. The results showed that using biodiesel slightly reduced the fuel economy and increased the brake specific fuel consumption (BSFC), which increased by 2.31%, 2.71%, and 2.04% for B10, B20, and B30 compared to B0, respectively. The study characterized the emission factors of CO, HC, NOX, and PN of agricultural tractors based on engine power aspects. Biodiesel helps to reduce the CO, HC, and PN emission factors of agricultural tractors by 10.15%, 12.73%, and 32.10% for B10, B20, and B30 respectively compared to B0 based on engine power; 13.22%, 26.45% and 30.58% for B0 based on power; and 8.22%, 10.91% and 30.58% for B0 based on power; and 8.22%, 10.91% and 30.58% for B30 based on PN emission. B0 power-based PN emission factors were reduced by 8.22%, 10.91%, and 14.17%, respectively. The reduction of CO, HC, and PN emission factors increased with the increase in biodiesel percentage. Biodiesel slightly increases NOX emissions from agricultural tractors, and as the proportion of biodiesel increases, the NOX emission factor increases accordingly, and the NOX emission factors for B10, B20, and B30 increase by 1.60%, 2.78%, and 4.20%, respectively, compared to those for B0 based on engine power. The power-based NOX emission factors of all tested fuels in this study were more than three times higher than the recommended values of the 《Guideline》, which shows that the recommended values of the 《Guideline》 do not apply to the NOX emission factors in the plateau environment, which affects the pollutant emissions of the tractor during the actual operation. To reduce pollutant emissions from agricultural tractors during actual operation at high altitudes, considering the fuel economy and the effect of biodiesel on NOX emissions, blending biodiesel in small proportions to be used as an alternative fuel for agricultural tractors can not only reduce CO, HC and PN emissions but also reduce the use of fossil fuels. The results of the study can provide a reference for the optimization of the actual pollutant emission control of biodiesel combustion in agricultural tractors in high-altitude environments and can supplement the emission database of agricultural machinery in high-altitude areas to assist environmental pollution research and policy formulation.