At present, clicking on the button and waiting for a period of time after completing the sketch fully is the most common recognition method for online sketched symbols. To achieve the continuous feedback, a primitive-based partial sketches recognition algorithm was proposed. In the stage of feature representation, the input strokes were segmented as primitives and then a new feature which presents the spatial relationship between a pair of primitives was come up with. Based on the model of assignment problem, symbols were recognized through the similarity of this feature finally. The proposed method is so easy that one can master it without training and it has nothing with the order of stroke, the number of stroke and the size of graph. Its validity was testified by experiment.