Nonlinear multiphoton absorption technology is crucial for developing novel optoelectronic devices and nanophotonics. The large enhancement of two-photon absorption (TPA) photoresponse by a high Q-factor whispering gallery mode (WGM) resonance based on a single-microwire (MW) self-formed hexagonal cavity was investigated comprehensively in this paper. The typical quadratic relationship of photocurrent as a function of incident power indicated that excited carriers resulted from a third-order nonlinear mechanism. Moreover, the photocurrent response had a dramatic dependence on the spatial location of the focus spot of the incident photons. It was demonstrated that the TPA photocurrent response in the resonant WGM mode was one-order of magnitude larger than the response in the Fabry-Perot mode. Furthermore, the photoresponse characteristics of TPA detection exhibited sensitive dependence on the incident laser polarization direction.