Due to their unique physical properties, nonlinear materials are gradually demonstrating significant potential in the field of optics. Gold nanoparticles supported on carbon black (Au/CB), possessing low loss and high nonlinear characteristics, serve as an excellent material for saturable absorber (SA) in ultrafast fiber lasers. In this study, we investigated the performance of Au/CB material and designed an ultrafast fiber laser based on Au/CB SA, successfully observing stable fundamental mode-locking and pulse bunch phenomena. Specifically, when the fiber laser operates in fundamental mode-locking state, the center wavelength of optical spectrum is 1 558.82 nm, with a 3 dB bandwidth of 2.26 nm. Additionally, to investigate the evolution of real-time spectra, the dispersive Fourier transform (DFT) technology is employed. On the other hand, the pulse bunch emitted by the laser is actually composed of numerous random sub-pulses, exhibiting high-energy characteristics. The number of sub-pulses increases with the increase of pump power. These findings contribute to further exploring the properties of Au/CB material and reveal its potential applications in ultrafast optics.