Abstract: As a road base, cement stabilized materials have the defects of low strength, easy to produce cracks and poor durability. Therefore, it is considered to add polyformaldehyde (POM) fiber to make composite solidified clay sand. The Box-Behnken response surface method was used for experimental design, and the unconfined compressive strength test, splitting strength test, water stability test and freeze-thaw cycle test were used to explore the performance improvement of composite solidified clay sand. The results showed that when the cement content was 5.47 %, the POM fiber content was 0.32 %, and the fiber length was 8.09 mm, the 7 d unconfined compressive strength of the solidified soil was the most obvious. The importance ranking of each single factor on the performance of solidified clay sand was: cement content > POM fiber content > POM fiber length. POM fiber could improve the splitting strength of solidified clay sand, enhance water stability and frost resistance. When the POM fiber content was 0.30 % and the fiber length was 8 mm, the splitting strength of solidified soil was the largest, and the water stability and frost resistance were significantly improved. The research results can provide reference for the performance improvement of clay sand in the Yellow River flood area.