To provide a flow rate characteristic function identification method, flow rate sensor, and flow rate characteristic function identification program that can set a flow rate characteristic function reflecting not only the type or shape of a fluid resistance but also the effects of states such as an attachment state of the fluid resistance, and calculate a flow rate with higher accuracy. An actual flow rate characteristic function, which is a flow rate characteristic function when an actual fluid resistance is provided in a flow path, is identified on the basis of multiple flow rate characteristic functions including a first reference flow rate characteristic function and a second reference flow rate characteristic function, and predetermined weighting.