The invention provides an online automatic detection system for aggregates. The online automatic detection system comprises a sampling device, a first detecting device, a second detecting device, a third detecting device, and a controlling device. The sampling device is used for obtaining the aggregate. The first detecting device is connected to the output end of the sampling device, and is used for drying the aggregate and detecting the quality of the aggregate before and after drying. The second detecting device is connected to the output end of the first detecting device, and is used for acquiring the image information of the falling of the aggregate and dusting the aggregate. The third detecting device is connected to the output end of the second detecting device, and is used for measuring the quality of the aggregate after dusting. The controlling device is connected to the first detecting device, the second detecting device, and the third detecting device, respectively, and is used for respectively calculating the moisture content, the grain shape and grain size information, and the dust content of the aggregate. According to the online automatic detection system for the aggregates, the real-time online detection of the aggregate condition on the production line can be carried out, and the moisture content, the grain shape, the grain size, and the powder content rate of the aggregate can be understood without manual intervention, which fundamentally changes the previous detection means.