Slope aspect is a major factor influencing biological soil crusts in arid and semi-arid areas. The majority of previous studies on slope aspect classification were relatively rough. It is still unclear how 360° continuous slope aspects affect biological soil crusts on roadside slopes. To explore the differentiation mechanism of biological soil crusts on different slope aspects and summarize their distribution, a roadside slope with 360° slope aspects in Hengshan District, Yulin City, Shaanxi Province, was taken as the research site. The road construction time, soil matrix, slope gradient and other background conditions were all the same. Biological soil crusts on the roadside slopes developed naturally. Based on this outstanding natural experimental site, the differences and causes of mixed biocrusts composition (moss and cyanobacterial crust coverage), developmental characteristic indicators (biocrust thickness, moss height, and chlorophyll a content of mixed biocrusts), water content of biocrusts and soil surface, and shear strength of biocrusts were studied at 15° slope intervals. The results showed that: (1) In the north-south direction, the mixed biocrusts in the 315°—30° range were dominated by moss crust, followed by cyanobacterial crust, while those in the 75°—225° range were dominated by cyanobacterial crust, followed by moss crust. Moss and cyanobacterial crust coverage along continuous slope aspects demonstrated a trade-off relationship. (2) In the east-west direction, the composition and development of mixed biocrusts exhibited an asymmetrical distribution pattern. Moss coverage of mixed biocrusts, water content of biocrusts and soil surface, and chlorophyll a content of mixed biocrusts were 3.31, 2.82, and 2.55 times higher on the western slope (225°—315°) than on the eastern slope (45°—135°), indicating better development on the western slope. (3) The water content of biocrusts and soil surface was related to the ratio of moss crust coverage and cyanobacterial crust coverage in mixed biocrusts. The water content of biocrusts and soil surface was lower than 3.8% when the cyanobacterial crust was dominant and higher than 7% when the moss crust was dominant. (4) The slope aspect showed a significantly positive correlation with the moss crust coverage, the water content of biocrusts and soil surface, and the chlorophyll a content of mixed biocrusts, while it exhibited a significantly negative correlation with the cyanobacterial crust coverage. The study reveals the differences and potential causes of composition and developmental characteristics of biological soil crusts on different slope aspects, which is helpful for accurately allocating cyanobacteria and moss on different slope aspects in ecological restoration project of biological soil crusts.