Abstract: In nature, the desiccation cracking of soils caused by water evaporation and shrinkage may lead to various engineering geological problems. The addition of biochar into the soil can effectively change its desiccation cracking characteristics. In this study, the effects of wood biochar dosages (0, 0.01, 0.03, 0.05, 0.1 kg/kg) on the desiccation cracking characteristics of Xiashu soil and red clay are investigated. The influence mechanism is demonstrated according to the microstructural analysis and the Atterberg limits. The results indicate that: (1) The effects of biochar on soil cracking significantly vary, depending on the type of the soils. For the Xiashu soil, the biochar accelerates the initial rate of cracking development, reduces the later cracking development rate and eventually inhibits the cracking. The inhibition effects are enhanced with the increase of the dosages, and the crack ratio is decreased by up to 32.2%. For the red clay, the biochar promotes the development of cracking significantly, especially in the presence of more biochar with the highest increase of 80.4%. (2) The biochar affects desiccation cracking characteristics of the soils in two ways. On the one hand, the biochar, as a non-plastic material, occupies the shrinkable space of the soils; on the other hand, it affects the thickness of hydration film of soil particles and affects the expansion of the soils. The combined effects of these two ways determine the cracking characteristics of the biochar-amended soils.