The gas-liquid two-phase flow is widely encountered in many industrial applications, and its online and nonseparation flow rate measurement has plagued the industry for many years. Based on the thermal diffusion measurement, which was proposed to measure the velocities and lengths of the Taylor bubble and liquid slug in our previous study, a method for further measuring the flow rate of gas-liquid two-phase flow under a slug flow pattern is presented in this paper. The pipe wall temperature is monitored to capture the passages of each Taylor bubble and liquid slug and measure their velocities (U-TB and U-LS) and lengths (L-TB and L-LS), based on which the liquid film thickness around the Taylor bubble (eta) is derived. A good linear relationship was found between the average descending slope of the temperature curve ((k) over bar), the liquid slug velocity (U-LS), and the void fraction in the liquid slug (alpha(LS)), and the void fraction is acquired based on this relationship. In accordance with the flow law and distribution of gas and liquid phases, a new flow rate calculation model is established to predict the flow rate of each phase using the measured slug flow characteristics (U-TB, U-LS, L-TB, L-LS, eta, and alpha(LS)). Experimental tests on air-water two-phase flow show that the average relative errors in the gas and liquid flow rates are 3.45% and 5.51%, with maximum values of 9.98% and 10.47%, respectively.