Recently, photoacoustic (PA) cavitation-mediated therapy has become the focus of research owing to its advantage of inhibiting drug or radiation resistance; however, its application is limited because it relies on nanodroplets with one-time action. Herein, we demonstrate a femtosecond-laser-pumped ultrafast PA cavitation technique for highly efficient shockwave theranostics using niobium carbide (Nb2C) coated with polyvinylpyrrolidone-40000 (PVP), producing sustainable PA cavitation with non-phase-change nanoprobes, which effectively gets rid of the dependence on nanodroplets, guaranteeing multiple treatments. Under femtosecond (fs) laser irradiation, given that the thermal confinement regime could be well satisfied, the Nb2C-PVP nanosheets (NSs) were quickly heated, forming localized overheated nanospots with the temperature exceeding the phase-transition threshold of the surroundings, leading to precise cavitation and explosion at the tumor sites. The experiments at the cellular level showed the significant anti-tumor effects of this method. Notably, the mouse model experiments showed a relative tumor volume inhibition rate of more than 90%, demonstrating the high precision and good efficacy of the proposed anti-tumor method. This method provides a sustainable and highly effective strategy for PA theranostics, indicating its great potential for clinical applications.