The invention discloses an approximate processing quality control method for online streaming data. The method comprises the steps that a sampling strategy for the streaming data of a current data processing window is determined, the streaming data is sampled according to the sampling strategy, and sampling data is obtained; the sampling data is approximately processed, a current approximate processing result is obtained, according to the user demand obtained in advance and the current approximate processing result, error analysis is conducted, and an error value is obtained; whether the error value is smaller than or equal to a preset error threshold or not is judged; if yes, the current approximate processing result is output, and if not, error correction is conducted. When the approximate processing quality control method is applied, the quality of the approximate processing result of the streaming data can be improved. The invention further discloses an approximate processing quality control device for the online streaming data. The device has the corresponding technical effects.