Experiments for the laser guiding studies has been carried out with the 30-fs 100-TW Ti:sapphire laser pulse interaction with the underdense plasma produced by a long-slab $(1.2 \times 10\ \hbox{mm}^{2})$ gas jet and an ablative laser-triggered discharged capillary. Formation of an extremely long plasma channel with a length ($\sim$10 mm) 10 times above the Rayleigh length is observed when the laser pulse power is much higher than the critical power for relativistic self-focusing. The long-self-guiding-channel formation is accompanied by the electron acceleration with a low transverse emittance $( ≪ 0.8\pi\ \hbox{mm mrad})$ and high electric current ($\sim$10 nC/shot), as well as the generation of a quasi-monoenergetic electron bunch with an energy of $\sim$ 80 MeV. In order to continuously elongate the plasma channel, a 4-cm-scale discharged capillary was used. We successfully demonstrated laser–plasma acceleration of high-quality electron beams up to nearly semigigaelectronvolts. Our results exactly verified the prediction of laser wakefield acceleration through a centimeter-scale plasma channel in the “blowout bubble” regime, where a microscale plasma cavity produced through the ultrarelativistic laser–plasma interactions plays an essential role in the self-injection and acceleration of electrons.