One of the most widely applied devices for repetitive pulse power generator is high-coupling Tesla transformer. The general designing of the high-coupling Tesla transformer is described in this paper. Because of the requirement of high coupling for Tesla transformer, an open-loop magnetic core is employed. In order to reach high reliability of this high-voltage generator, the windings of Tesla transformer (both primary winding and second winding) are set compactly within the insulating gap of pulse forming line (PFL). The parameters of primary and secondary loops have be well-connectedly designed and suitably adjusted. Moreover, as one of the most important components of the TPG700, a high-coupling Tesla transformer, with open-loop magnetic core applied in it, achieved a high efficiency about 83% after optimization. This Tesla transformer can operate on the range of repetition frequency from 1 to 100 Hz.