Two composite soil amendments were prepared by blending waste wood-derived biochar(WBC) and municipal sewage sludge compost(SS) with polyacrylamide(PAM) and nano-silica(SiO2-NPs) at the mass ratios of 42.5∶42.5∶4∶11 (BCS1) and 42.5∶42.5∶8∶7(BCS2), respectively. The effects of WBC, SS, BCS1 and BCS2 on oil sunflower (Helianthus annuus L., a typical salt-tolerant commercial crop) growth and salt-affected soil(collected from the Yellow River Delta) remediation were evaluated via pot experiment. The results showed that the composite amendments prepared by combining WBC and SS effectively integrated carbon sequestration, nutrient regulation, and structural optimization. The directional loading of SiO2-NPs and PAM reconstructed surface functional groups(e.g., Si—O—-Si and C=O bonds), leading to distinct physicochemical properties of BCS1 and BCS2 compared with WBC and SS alone. BCS2 exhibited better water retention performance, increasing the soil maximum water holding capacity(WHC) by 11.32% compared with the blank treatment without amendment(CK), which effectively improved the soil water retention. Compared with CK, the addition of 4 amendments promoted the photosynthesis and growth of oil sunflower, with leaf SPAD significantly increasing by 6.83%-11.44%. Compared with WBC and SS, BCS1 and BCS2 had stronger promoting effects on photosynthesis. The effect of BCS2 on plant growth was better than that of BCS1. The addition of BCS2 significantly increased the stem diameter by 19.57% and the number of root tips by 238.13%. These effects were mainly attributed to improve soil aggregate stability(the mean weight diameter of rhizosphere and non-rhizosphere soil aggregates of BCS2 increased by 18.18% and 18.98%) and enhance water and nutrient availability, resulting in significantly increases in available phosphorus(AP) in rhizosphere and non-rhizosphere soils by 25.36%-84.22% and 12.45%-64.63%, respectively, thereby improving soil health. Furthermore, the results of structural equation model analysis revealed that amendments indirectly enhanced plant growth primarily by increasing WHC, followed by soil nitrogen, carbon, and aggregate stability. It could be seen that the composite amendments prepared from WBS and SS products demonstrated high potential for coastal salt-affected soil remediation.