The photothermal effect in graphene offers advantages such as broad response bandwidth, high sensitivity, rapid response speed, and strong integration capability, making it a promising candidate for developing high-performance terahertz detectors. In this study, a new type of terahertz detector is designed by organically integrating two different types of photothermoelectric detector configurations, namely, dual-gate modulation and asymmetric source-drain electrode structure. This synergistic integration significantly enhances the detector's overall performance. Experimental results demonstrate that the detector achieves a responsivity of 50.48 V/W under 0.3 THz illumination, with a response time of 25.74 μs and a Noise-Equivalent Power(NEP) of 235.37 pW/Hz^1/2.