An experimental study of two photon absorption(TPA) in the HgCdTe pn junction detectors was reported. The excitation light source was a picosecond pulsed infrared laser. Even the incident photon energy was about 60% of HgCdTe(MCT) bandgap, an obviously photo-response was still observed. Quantification dependence of the peak amplitude on the incident intensity presented a slope of 2 by linear fitting to the experimental data in log-log coordinate, which indicated that the photo-response exhibited a quadratic power dependence on the incident intensity, suggesting a typical TPA process. The two photon absorption coefficient(TPAC) inside the space charge region(SCR) is as high as 130 times that of outside the depletion region which can be attributed to the TPA Franz-keldysh effect.