Abstract: Aiming at the non-contact measurement of flow field in narrow channel of plane cascades, a two-dimensional flow field measurement method based on ultrasonic velocity difference measurement is proposed. A 2×4 ultrasonic transducer array with a combination of bevel and flat transducers is designed, and then multi-channel ultrasonic measurement and velocity field reconstruction systems are developed. The flow field measurement experiment for plane cascade is carried out, and the two-dimensional velocity fields of flow channel under three inlet velocity conditions are obtained. The CFD module in COMSOL Multiphysics is selected to carry out the numerical simulation of cascade flow field synchronously, which is compared with experimental data, showing close results with deviations within 5% for velocity and deflection angle, respectively. The flow characteristics of cascade passage are also reflected by numerical and experimental methods. The present ultrasonic method can be expected to be applied to the measurement of high Mach number flow field.