The invention relates to an unbalance load preventing system and method for throwing unloading of a railroad loading station. The system comprises an unloading gate of the loading station and an unloading chute provided with a discharge gate, a carriage speed detector, a carriage position detector, a chute material stock detector and a gate position detector are connected with an unbalance load preventing controller, the unbalance load preventing controller is also connected with an expert database and a train number reader and is connected with a train speed controller, an unloading chute controller, a discharge gate controller and a loading station host computer. By means of calculation of a loading carriage and cargo quantity in advance, an ideal balanced loading state is obtained, loading is executed according to the ideal state during loading, meanwhile, the loading state of the carriage is continuously monitored, and the loading state is adjusted to be close to the ideal state asfar as possible until the loading is ended. The probability of unbalance load is reduced to be minimum, full automation of loading is realized, and manual high-intensity work for flat cars after loading and risks of safety problems are reduced.