The utility model discloses a float drilling platform of a bridge in-water foundation, which comprises a floating pontoon and a flexible anchorage structure, the floating pontoon is equipped with a combined portal crane and a combined drilling platform, a thrust and suction drilling machine is mounted on the drilling platform, a vacant position is located on the float drilling platform, and a steel casing is inserted at the vacant position. Because the floating drilling platform and the steel casing are respectively in an independent system, the drilling quality is not affected by shaking of the platform, a limiting device at the upper end port of the steel casing guarantees high accuracy of drilling, the thrust and suction drilling machine is utilized, thereby being low in investment and light in weight without being affected by water rising and water falling, and is low in occupied area, the thrust and suction drilling machine doesn't generate horizontal torque to the floating drilling platform, enables quantity of the anchorage to be reduced, and is favorable for drilling accuracy, and the thrust and suction drilling machine is used on the floating platform, thereby being capable of overcoming shortages of unstable hole-bottom drilling pressure while using a rotating drill machine on the floating platform.