The invention relates to a method for improving the soil fertility through kitchen waste organic acid fermentation liquor, and belongs to the field of soil improvement. The method comprises the steps that firstly, kitchen waste is pretreated, and smashed after being blended with water with the solid-to-liquid ratio being 1:1-1:2, so that kitchen waste slurry is obtained; secondly, an anaerobic fermentation tank is loaded with the kitchen waste slurry for anaerobic fermentation at the room temperature, and the kitchen waste organic acid fermentation liquor is obtained; and the kitchen waste organic acid fermentation liquor in the anaerobic fermentation tank is taken out, centrifuged or press-filtered, after supernate is filterd out of a film, and a fermentation liquor liquid fertilizer is obtained and used for improving the soil fertility. Compared with the prior art, the kitchen waste used in the method is low in price and easy to obtain, and waste utilization is achieved. The fermentation liquor liquid fertilizer obtained through the method can be used for increasing the contents of nitrogen, phosphorus, potassium, amino acid, organic acid and protein in soil, enhancing the effect of killing pathogenic bacteria in the soil, improving the microbial flora structure of the soil, and improving the soil fertility. According to the fermentation liquor liquid fertilizer obtained through the method, operation is easy, and large-scale preparation can be achieved.