Abstract: Abstract: At present, plug seedling cultures are common in China. The traditional plug has a hole on the bottom, which could cause the root growing through the bottom hole, thus the roots will be easily hurt when moving and plug needs to water frequently, which wasted water. In order to solve these problems, Beijing Vegetables Research Center（BVRC）developed the side opening plug, open double vertical holes surrounding each plug, each vertical hole is not lower than the bottom of the plug, which would help by keeping water in the plug. At the same time, it could avoid the roots growing through the bottom. To understand the effects of this new side opening plug method, tomato (Solanaceous vegetables) was used as the test materials in this paper. And we observed the effects of different opening methods in summer on seedlings' growth, development and water use efficiency. The main contents are as follows: Tomato cultivar 'Ouguan' was used as materials, to study the effects of the side opening and bottom opening plug methods on seedlings' growth and water use efficiency in summer. The test had two treatments, bottom opening and side opening; each treatment was repeated 4 times. In order to precisely control the amount of watering, the water was injected to each plug by a gun. The lower limit for irrigation was substrate water content decreasing to 50% of the maximum moisture capacity. Irrigation lower limit and upper limit was determined by the weighing method. Every time before and after irrigation, the weight of the trays were recorded. The amount of water irrigated and the outflow water were recorded. We also recorded the plant growth index. The results showed that the seedlings in side opening trays grew better than those in bottom opening trays in summer and autumn. The seedlings growing in side opening plug are higher and thicker with a larger biomass and higher seedling index (0.0178, 22.76%). During the whole seedling stage, the average watering amount is 25.58 kg of the side opening plugs, which is 11.7% less than bottom opening treatment. The results have shown that, the side opening plug method could promote the seedling growth and save water. The new tray supplies the seedling with a better environment, including water, fertilizer, gas and temperature, which make the tomato seedlings grow well, effectively increasing the biomass of the seedlings and seedling index. The new tray can also reduce the use of water and save labor.