A discharge location detection system was designed and implemented, and it was applied to study the basic mechanism governing wire breaking and the effects of machining conditions on the vertical straightness of machined part in WEDM process. Experiments were conducted under an inappropriate water flushing and a large feed rate conditions. It is confirmed that wire breaking is attributed to an increasing discharge frequency together with a high proportion of abnormal discharges taking place in the vicinity of the same location. It is also found that the commonly obtained concave shape cross section of the machined part is closely related to the distribution of discharge along the workpiece height. The discharge locations are more uniformly distributed and there is less barrel shape cutting kerf under a higher feed rate or a smaller discharge off-time condition. The distribution of the discharge locations shifts downward if the lower water pressure is reduced. In addition, the developed discharge location detection system can be used for on-line estimation of the shape and workpiece height. For a varying heights workpiece with maximum thickness of 50mm, the time required for every estimation cycle is only 0.03 sec, the shape is accurately obtained, and the estimation error is within 2mm.