Abstract: This research develops a tidal level measurement technique based on stereosopic photography, which does not require any sea surface control points. Firstly, the technique determines an equipotential surface P and gravity direction near the true average sea surface with a sequence of images collected in a short period of time, and then uses stereoscopic photography wave measurement technology to measure the sea surface displacement changes caused by waves to further determine the relationship between the average sea surface and equipotential surface, thus achieves tidal level variation. The research presents a geometric model of stereoscopic photography for tidal level measurement as well as the control equations and corresponding algorithms for each part of the model. Based on a 26-day validation experiment conducted on the Bohai Sea oil platform, a set of experimental image sequences, the calculation method and results of the model were verified in details. It shows that, compared to traditional tidal level gauge measurements, 50% of measurement points have measurement errors within 2 cm, 73.6% of them have measurement errors within 4 cm, 88.8% of them are within 6cm, and only 4.5% of them are greater than 8 cm, demonstrating the accuracy and feasibility of this technology. Since the technology does not require calibration of sea surface control points, its is easier to operate, more economical, and not easily damaged by fishing activities, and thus can compensate some shortcomings of traditional tidal level monitoring equipment.