The Loess Plateau is known as a famous climate-sensitive zone and a fragile ecological environmental belt in China. A variety of environmental factors, such as soil type, geographic location, climate, etc., constrain the accumulation of soil organic matter in this region. Thus, quantifying the spatial distribution of soil organic carbon (SOC) and its fraction is significant for better understanding on soil carbon cycle across the Loess Plateau region. Soil humus, as the major soil organic matter component, is a key indicator for the soil quality and fertility. Yet, the distribution characteristics of soil humus and its fractions across the Loess Plateau have been paid little attention and still remain big uncertainty. In this study, we characterized the vertical distribution of humus and its fractions including Humic Acid (HA) and Fulvic Acid (FA) in the 0-200 cm soil profile along south-north gradient in the Loess Plateau. Then, we further explored the correlations among soil humus, HA, FA, soil total nitrogen, and soil particle composition. An intensive field campaign was conducted to collect 132 soil samples in some typical sites from the south to the north of the Loess Plateau. The results show that the contents of humus, HA and FA, varying among soil types and along soil profiles, are lower than those in other regions of China reported in previous studies. A decreasing gradient from the south to the north of the Loess Plateau is observed for the contents of humus and its fractions. Along the soil profile, the contents of humus, HA, and FA decrease with depth 0-60 cm, slightly decrease with depth 60-120 cm, and remain low and stable below 120 cm soil layers. The fractions of soil humus in SOC increase from the south to the north of the Loess Plateau, ranging from 26.6% to 54.7%, which is lower than that in other regions across China. However, these observed fractions in the same sites have no significant difference in the entire profile. The fractions of HA in soil humus are 39.8%, 49.0%, and 53.5%, respectively, and the HA/FA ratios are 0.66, 0.96, and 1.15, for 0-40 cm, 40-120 cm and 120-200 cm soil profiles, respectively, for Emn-Orthic-Anthrosol soil type. The fractions of HA in humus are 26.3%, 33.9% and 42.3%, respectively, and the HA/FA ratios are 0.36, 0.51, and 0.73, for 0-40 cm, 40-120 cm and 120-200 cm soil profiles, respectively, for Los-Orthic-Entisol soil type. The fractions of HA in humus are 13.4%, 37.1% and 45.2%, and the HA/FA ratios are 0.16, 0.59, and 0.82, for 0-40 cm, 40-120 cm and 120-200 cm soil profiles, respectively, for Ust-Sandiic-Entisol soil type. This study indicates that all typical soil types that were observed from the south to the north of the Loess Plateau are FA-enriched; the humus quality is relatively poor compared to other regions in China and decreases gradually from the south to the north of the Loess Plateau. Finally, the contents of humus, HA, and FA are significantly (P< 0.01) correlated with soil total nitrogen content. On the other hand, the contents of SOC, humus, and HA are significantly (P< 0.01) correlated with soil sand and clay contents.