The invention discloses a cylindrical foundation reinforcing method for an offshore platform. The method is characterized in that: a cylindrical foundation mainly provides anti-pressing and anti-pulling bearing capacity for the platform, a steel pile is driven into a manhole of the cylindrical foundation, the length of the steel pile extends out of one part of the top of the cylindrical foundation, and a pile fixing sleeve for solidification is arranged at the top of the steel pile. The pile fixing sleeve is in a tubular structure, the bottom of the pile fixing sleeve is provided with a base, the clearance between the pile fixing sleeve and the steel pile is filled by using cement paste, and the soil-free part of the interior of the cylindrical foundation is also filled by using the cement paste. The solidified pile fixing sleeve mainly transfers the pressure and the pulling force on the cylindrical foundation to the steel pile in the manhole of the cylindrical foundation. A shear key is arranged between the pile fixing sleeve and the steel pile, the cement paste and the shear key share the pressure on the cylindrical foundation together, the base at the bottom of the pile fixing sleeve is used for transferring the pulling force on the cylindrical foundation to the steel pile in the manhole, the paste needs to be filled into the base, and the paste and stiffening plates in the base share the load transferred by the cylindrical foundation together, so the problem of insufficient bearing capacity of the cylindrical foundation is solved.