The invention relates to a research method for growth dynamic conditions of a plant root system, in particular to a method for monitoring plant root system growth in a horizontal mound layering process of apple stocks. The method comprises steps as follows: the annual apple stocks are horizontally planted in the ground in spring, buds on the back of the plants are processed and are accelerated to germinate before germination of the stocks, a quantitative number of appropriate new shoots is reserved when the new shoots grow to 15 cm, a minirhizotron is horizontally arranged between the stocks and covered with saw dust, and the rooting condition and the late root system growth dynamics in the horizontal mound layering process of the apple stocks are monitored by a root system scanning instrument regularly. According to the method for monitoring the plant root system growth in the horizontal mound layering process of the apple stocks, the growth dynamic condition of a seedling root system in the horizontal mound layering process of the apple tree stocks is researched, direct observation for the seedling root system and rapid and accurate measurement and analysis for morphological parameters are realized, and the direct, efficient and reliable research method is provided for screening of the apple stocks with the high propagation coefficient in the horizontal mound layering process.