The invention provides a Rieger begonias organic substituted matrix and a soilless culture method thereof. The soilless culture method is established according to different quantity demands on moisture and nutrient at the different growth and development stages of the Rieger begonias under the condition of Rieger begonias organic substituted matrix culture. The matrix and the method are used for the soilless culture of the Rieger begonias, can enable the growth rate of plants to be faster, the growth vigor to be healthier and stronger, and the blooming period to be longer compared with the conventional culture method, and reduce night soil consumption and production cost.