This paper concerns hydraulic performances of a vertical gate to free and submerged underflows in the light of the one-dimensional treatment of hydraulic analysis. For the free underflow, main emphasis is placed on the contraction of efflux influential to the stage-discharge relationship for practical uses, through a thorough research of past works added to by further experimentations by the authors. A possible scale effect in physical simulation for the present problem will be also explained. For the submerged underflow, the transition problem from free to submerged flow at the gate will be accented. Some discussions of the discharge coefficient of the gate to the submerged underflow are also made