A new mobile parabolic thin-plate weir for U-shape channel flow measurement was developed, the height difference between upstream water and backwater and critical submerged ratio is analyzed, the allowable sectional area ratio of flow measuring weir to the U-shape channel is obtained, the formulae for calculating the discharge and the law of the discharge coefficient are put forward. The results reveal that the new mobile parabolic thin-plate weir with high measurement accuracy, simple structure, low cost and easy to use, can be used for small U-shape channel flow measurement.