The tomato variety “Yuyi Jinfen No.2” and cucumber variety “Yuyi201” were used as the test materials. Peat∶ vermiculite∶ perlite = 1∶1∶1 (volume ratio) was used as cultivation medium and plug seedling was carried out. The effects of different concentrations (0，25%，50%，75%，100%) of rice chaff ash extracts on the physicochemical properties of substrate and the growth of tomato and cucumber seedlings were studied. The results showed that: compared with the control，the water-holding porosity and aeration porosity of seedling substrate were significantly increased by applying 75% rice chaff ash extract，and the physicochemical properties of substrate were improved. With the increase of the concentration of rice chaff ash extract，the amount of microorganisms in the two substrates was basically the same，and the amount of bacteria and fungi showed a downward trend. Compared with the control，the plant height，stalk width，root shoot ratio and strong seedling index of tomato and cucumber seedlings were significantly increased，and the chlorophyll content，net photosynthetic rate，stomatal conductance and transpiration rate of seedlings were also significantly increased by root application of rice chaff ash extract，and 75% rice chaff ash extract was the best. In addition，root application of 75% rice chaff ash extract could increase the contents of total soluble sugar content，sucrose content and the activities of key enzymes in leaves. It can be seen that rice chaff ash extract can effectively improve the physiochemical properties of substrate，promote the growth and photosynthesis of plants，and improve the carbohydrate metabolism of seedlings. The best concentration of rice chaff ash extract is 75%.