To verify the necessity of the time synchronization mechanism in a multibaseline synthetic aperture radar (SAR) system and to acquire the allowable magnitude of the residual time synchronization error after compensation, the influence of the time synchronization error on the altimetry accuracy of multibaseline SAR is studied. Based on a time synchronization error model, the influence of the time synchronization error on the interferometric phase and the influence of the interferometric phase error on the altimetry accuracy of the multibaseline SAR are analyzed, and accordingly, an error transfer model from the time synchronization error to the altimetry accuracy of the multibaseline SAR is established. According to the established error transfer model, the necessity of the time synchronization mechanism in the multibaseline SAR system is verified, and a formula of the allowable magnitude of the residual time synchronization error is derived. The formulas of the single-baseline SAR and the multibaseline SAR to evaluate the altimetry accuracy are compared, and the condition that the altimetry accuracy of the multibaseline SAR is higher than that of the single-baseline SAR is clarified. The accuracy of the derived formula is verified by the performed simulation.