This contribution describes a method for measuring diffraction peaks of a standard sample to estimate the incident X-ray wavelength at the 1W2A SAXS beamline at BSRF. A simple simulation has been performed to establish the factors influencing the accuracy of the wavelength measurement. Appropriate measurement conditions and error control measures are presented. An actual experimental example further verifies the effectiveness of the simulation. This method is particularly suitable for synchrotron radiation beamlines using bent triangular crystal monochromators.