A method and system for sampling input data. The method includes: buffering input data; recording an execution path of the buffered input data in an online operation module; determining whether the buffered input data passes through a desired execution path, and responsive to the buffered input data passing through the desired execution path, sampling the buffered input data to a data set. The system includes: buffering means for buffering input data; recording means for recording an execution path; sampling means for determining whether the buffered input data passes through a desired execution path.