We experimentally demonstrated a novel photocontrol scheme of a microbubble. The microbubble was confined in a fiber-based hollow microstructure and its movement was driven by the laser-induced photothermal Marangoni force. The position of the microbubble was controlled at a micrometer scale by simply adjusting the drive laser power. This scheme permitted the firsthand control of a microbubble with a divergent single laser beam. As a practical demonstration, we proposed a variable fiber all-optical attenuator by exploiting the total internal reflection on the surface of the photo-controlled microbubble to modulate the target light beam. The experimental results showed that such a compact fiber attenuator possessed a low insertion loss of 0.83 dB, a maximum extinction ratio of 28.7 dB, and had potential to be integrated into the lab-on-a-chip for the modulation of the light beam power.