In the field of measuring the laser power, the traditional way is direct measuring based on thermal effects. In this method, the laser power can be measured from the temperature change of the sensor absorbing the laser light. However, it is difficult to operate when the power exceeds 10kW level because of the linearly scaling size of absorbing object and the relatively long recovery (cooling) periods, which results in the proposal and fast development of indirect measuring technique route. Using light pressure to measure laser power is one of the recent research hotspots of indirect measuring. The typical system design is a scale attached with a nearly perfect mirror that had shown the advantages such as high accuracy, fast response, real-time measuring and convenient calibration. Nevertheless, the commercial mirror (with a reflectivity of 0.997 as a typical value) and scale (with a 100nN resolution as a typical value) cannot achieve a stable measuring due to the feeble light pressure. In fact, the measuring uncertainty could be 7%-13% in practical operation. So it is reasonable and feasible to amplify the light pressure. In this paper, we propose a new structure design based on oscillation cavity which can improve the energy utilization and increase the number of reflections. The force measured by our system is expected to be 50 times more than that imparted by single reflection if the reflectivity of the mirrors installed on the oscillation cavity is larger than 0.99. This novel method can not only achieve higher sensitivity but also retain the advantages of indirect measuring such as fast response, real-time measuring. The resolution ratio could be at the level of 1W using the same scale as the sensor. The theoretical principles and system design will be introduced and analyzed in detail.