Improving agricultural productivity in saline soils is crucial for securing food supplies, especially in the context of global food security challenges. In this study, cellulolytic bacteria and plant growth-promoting rhizobacteria (PGPR) were isolated from saline soils and combined with vinegar residue for preliminary composting. The resulting compost was then enriched with indoleacetic acid to produce a vinegar residue compound biofertilizer. The impact of co-applying vinegar residue compound biofertilizer and modified biochar on saline soils was evaluated through plant potting experiments. Compared to untreated soil, this co-treatment treatment significantly enhanced soil quality. It reduced soil pH by 0.59 units, increased organic matter content to 20.20 g/kg, and boosted the levels of available nutrients: alkaline nitrogen increased by 71.67%, available phosphorus by 125.30%, total nitrogen by 83.33%, and total phosphorus by 90.91%. Enzyme activities also show substantial increases, with urease activity rising by 66.79% and alkaline phosphatase activity by 141.13%. Moreover, the co-application of vinegar residue compound biofertilizer and modified biochar markedly promoted the growth and photosynthesis of wheat seedlings, resulting in a maximum increase in fresh weight by 109.09% and dry weight by 133.3%. This study presents a viable approach for improving saline-alkaline soils, contributing to food security by significantly enhancing agricultural productivity.