Abstract: A method is presented for measuring two-dimensional unsteady flow velocities with X-hot-wire probes.Based on the well-known calibration law incorporated with the yaw angle correction function f(θ) = cosmθ, the magnitude and the direction of the velocity are determined. The applicable range for this method and the errors caused by variation of parameter m with flow angles and velocities are also discussed.Since no approximation is introduced in the calculation,the accuracy of measurement is enhanced. This method can be employed where the magnitudes and the directions of the velocities vary to a great extent. Moreover, the formula provided is simple to use.