The objective of this study is to investigate effects of discharge uniformity on acceleration performances of MHD accelerator. In order to demonstrate this, two types of experiments were conducted. First, "constant voltage experiment" was conducted. The objective of this experiment was to confirm reproducibility of experimental data obtained in previous one. The results have indicated that the velocity augmentation depends on discharge uniformity and that it is large for uniform discharge. Secondly, "constant current experiment" was conducted. its experimental objective is to clarify the relation of discharge uniformity and acceleration performance under constant current, in other words under constant Lorentz force. The result has suggested that the velocity augmentation becomes large and at the same time, acceleration efficiency tends to increase as the discharge becomes uniform. Moreover, the data obtained at wide range of plasma fluctuations have indicated clearly that the velocity augmentation increases as the discharge becomes uniform.