[Objective] The effects of 12 different exogenous organic materials， including tobacco stalk biochar， fruit tree branch biochar， wheat straw， rapeseed straw， chicken manure， cow manure， glucose， cellulose， LB medium， polyacrylamide （PAM）， humic acid fertilizer and chitosan， on the physicochemical properties and soil organic carbon fractions of typical loess （black loessial and loessial soils） were studied to provide a theoretical basis for selecting and applying organic soil conditioners to improve the quality of cultivated soil. [Methods] Organic materials were mixed with air-dried soil at a mass ratio of 3%， and a 100-day indoor incubation experiment was conducted using a control group （CK） without organic material addition. Density flotation combined with wet sieving was used to separate and quantify four organic carbon fractions： free particulate organic carbon （FPOC）， occluded particulate organic carbon （OPOC）， particulate organic carbon （POC）， and mineral-associated organic carbon （MOC）. Redundancy analysis was performed to analyze the relationships between soil physicochemical properties and organic carbon fractions. [Results] ① Compared with CK， the addition of organic materials effectively reduced the calcium carbonate content of the two typical loess soils and increased the soil electrical conductivity， TOC and total nitrogen （except for cellulose addition）. ② Compared with CK， the contents of FPOC， OPOC， POC， and MOC in the soil increased， with the largest increments in FPOC observed under treatments with fruit tree branch biochar， tobacco stalk biochar and wheat straw. In black loessial soil， the corresponding indicators increased by 2 158.5%， 1 545.3%， and 907.5%， respectively， whereas in loessial soil， the increases were 2 971.8%， 1 717.9% and 1 730.8%， respectively. ③ A highly significant positive correlation was noted between FPOC， OPOC， POC， MOC contents and TOC （p0.01）. The C/N ratio and total nitrogen content were the primary factors influencing the organic carbon content of the soil components， with explanation rates reaching 76.1% and 76.3% in black loessial and loessial soils， respectively. [Conclusion] The addition of organic materials increased TOC content， and effectively improved soil physicochemical properties. Compared with CK， the contents of FPOC， OPOC， POC， and MOC in the soil increased. The C/N ratio and total nitrogen content were the dominant factors influencing the organic carbon content of the soil components.