Taking solidified phosphorus slag as filler for roadbed or pavement base is an effective way to utilize solid waste resources, which has wildly economic benefits and social value. In this paper, the road performance of phosphorus slag- cement composite filler was analyzed in terms of strength and water durability through laboratory and on-site tests. Then, the availability of the solidification method was discussed through specific engineering cases. The test results indicate that under weak alkali activation ( pH = 8. 0), the compacted phosphorus slag mixture can form a solidified body, whose strength could meet the requirements of roadbed filler. However, strength incensement of solidified body is relatively slow. The compressive strength of solidified body after 7 d is about 50% of the compressive strength after 28 d. The solidified phosphorus slag-cement composite filler is water resistance. Once the cement clinker content is greater than 7% ( mass fraction), the damage that affects the integrity of the sample cannot be observed during a 60 dfree soaking, and the softening coefficient of the solidified sample decreases as the content of cement increases. Moreover, keeping the strength as a constant, using curing agent (Na2 SiO3 ) can save the amount of cement used and improve the economic efficiency of solidification method. Excessive alkali activation (pH = 10. 0) can only improve the early strength of solidified body and has little effect on the 28 d strength. Finally, the on-site engineering practice shows that the weak alkali-activated phosphorus slag solidification method can effectively reuse of phosphorus slag resource, which has strong generalizability in highway roadbed and pavement base filling engineering.