In order to improve the unconfined compressive strength of expansive soil and reduce engineering hazards. Based on the research of lignin-improved expansive soil, the influence of fiber length, fiber content and lignin content on the compressive strength of expansive soil was studied through univariate experiments, and based on the results of single-factor tests, the response surface test was carried out by BBD response surface design method, and a quadratic regression model was established, and the influence of two-factor action on the unconfined compressive strength of expansive soil was studied. The results show that under the univariate action, the unconfined compressive strength of expansive soil shows a trend of first increasing and then decreasing under all factors. When the two-factor interaction occurs, the interaction between lignin content and polypropylene content is the most significant. The optimal combination obtained by the BBD response surface method was as follows: polypropylene fiber length was 9 mm, fiber content was 0.3%, lignin content was 3%, and the average compressive strength of the parallel test group was 552.48 kPa, which was increased by 76.97% compared with the compressive strength of prime expansion. It can be seen that the compressive strength improvement effect of prime expansion is the best under this scheme.[ ]