The invention relates to an in-tunnel fast-turning construction device and method for mechanical-method multiple connecting channels. The method includes the following steps that a movable platform capable of moving along a tunnel is arranged in the tunnel; a pipe jacking machine is put on the movable platform; the pipe jacking machine is moved to a to-be-constructed position through the movable platform, and a connecting channel for connecting two tunnels is advanced and constructed; a movable platform in another tunnel moves to the corresponding position and receives a pipe jacking machine;the movable platform is rotated, and the pipe jacking machine is reversed and moves to a next construction position; another connecting channel is advanced and constructed; the pipe jacking machines are received through the movable platforms in the corresponding tunnels and are reversed, and other connecting channels are constructed by repeating the steps. According to the in-tunnel fast-turning construction device and method for the mechanical-method multiple connecting channels, the construction speed of the tunnel connecting channels is increased while the construction safety of the connecting channels is guaranteed, and the in-tunnel fast-turning construction device and method have the advantages of being safe, reliable, economical, efficient and high in adaptability.