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Metasurface, with the ultrathin thickness, has been extensively investigated in the past few years. A specific branch, the metasurface-based absorber, has generated considerable interest as a result of its high absorptivity of electromagnetic waves. In this paper, an ultra-wideband absorber based on patterned phosphorene metasurface is proposed in terahertz range and can overstep the bandwidth limitation of the conventional metasurface-based absorber. This absorber comprises 4-group phosphorene/dielectric pairs with various widths and regular spaces, which forms frustum pyramid stack on a gold ground. In this design, the surface plasmonic waves are excited on phosphorene and the wide bandwidth from 3.4 to 9.6 THz with the absorptivity ≥90% is obtained. Attributing to the electric dipolar resonance, the incident plane waves with various frequencies are absorbed at phosphorene with corresponding widths, which results in the ultra-wideband absorption. Moreover, it remains ultra-wideband and high absorption over a wide angular range of incidence around 40°, and an absorption band above 90% even for 70° incident angle. The proposed phosphorene-based absorber has potentials in THz detectors, thermal emitters, etc. [ABSTRACT FROM AUTHOR]