Desiccation shrinkage is a key factor contributing to the engineering hazards in expansive soil. To inhibit the initiation and expansion of cracks, a composite improvement approach using biochar and sisal fibers was applied to expansive soil from Nanning, Guangxi. An orthogonal test method was employed to conduct desiccation cracking tests on the improved soil, investigating the effects of biochar and sisal fibers on crack length, crack ratio and crack width. The results indicate that different proportions of sisal fibers and biochar can effectively inhibit soil crack development. The biochar content is the primary factor affecting crack length, while sisal fibers mainly inhibit the development of crack ratio and average crack width. The optimal proportion for composite improvement approach was found to be 6‰ of 3 cm sisal fibers and 4% biochar. The study findings can provide a new approach for the expansive soil improvement and for controlling engineering problems caused by soil cracking.