The invention provides a chainless water-assisted power bicycle. The bicycle comprises a motion device, a bicycle body bracket, and a drive device; the motion device includes a front wheel, a rear wheel, and a braking device; the drive device includes foot pedals, an active hydraulic pressure machine, a passive hydraulic pressure machine, an active liquid infusion pipe, a passive liquid infusion pipe, and a liquid storage pipe; the foot pedals are mounted on two sides of the active hydraulic pressure machine, the active hydraulic pressure machine is mounted on the bottom of an inverted triangle bracket, the passive hydraulic pressure machine is mounted on the bottom of a rear wheel support bracket and connected coaxially with the rear wheels, the active hydraulic pressure machine and the passive hydraulic pressure machine are connected with both the active liquid infusion pipe and the passive liquid infusion pipe at the two ends respectively, the liquid storage pipe is located in a pipeline of the passive liquid infusion pipe, and an injection mouth is formed in the liquid storage pipe. Through simulation of the working principle of an automobile engine and the principle of a jack, in combination with the mechanical structure framework of the bicycle, taking water as a power transmission medium and utilizing the pressure transmission effect of the small-radial active hydraulic pressure machine and the large-radial passive hydraulic pressure machine, the chainless water-assisted power bicycle is capable of achieving the goals of saving effort, efficiency, green travel, health, and environmental protection.