Compared with other flow patterns, wet-gas pseudo-slug flow is characterized by highly unstable gas-liquid interfaces and complex,variable spatiotemporal distributions, posing significant challenges to online, non-separative flow measurement in the oil and gas industry. To address this issue, this study proposes a combined sensor consisting of a microwave resonant cavity and a Venturi tube. The microwave resonant cavity sensor is used to characterize phase holdup, while the differential pressure signal from the Venturi sensor is employed to reflect the total flowrate of the fluid. Dynamic experiments are conducted based on this combined sensor, and a pseudo-slug flow generation device is designed upstream to enable independent control of the pseudo-slug length and occurrence timing. Experimental results show that the microwave amplitude signal and differential pressure signal exhibit pronounced periodic characteristics, which are highly consistent with the pseudo-slug occurrence cycle in the time domain. The arrival of pseudo-slugs induces abrupt changes in both the microwave amplitude and Venturi differential pressure. Furthermore, the effects of different operating conditions, including water cut, pressure, and gas-phase velocity, on sensor response characteristics and measurement performance are systematically analyzed. To reduce modeling complexity, the pseudo-slug flow is divided into two stages, namely “conventional wet gas” and “pseudoslug body.” Gaussian process regression is then employed to establish separate models for volumetric water holdup and apparent flow rate. The results indicate that, at a 90% confidence level and within the experimental conditions considered in this study, the relative prediction errors of water volume fraction and gas flowrate for the “conventional wet gas” stage are ±13.2% and ±2.2%, respectively, while those for the “pseudo-slug body” stage are ±14.8% and ±9.04%, respectively. The results provide an effective technical pathway for online, non-separative flow measurement of wet-gas pseudo-slug flow in natural gas production.