The invention discloses a method for repairing and strengthening a bridge pier damaged by collision under a no-unloading condition on a coastal wharf. The method comprises the steps that loose concrete on a damaged pile is firstly cleaned away, and water accumulated inside the damaged pile is extracted; concrete is poured into the hollow part of the damaged pile for repairing and strengthening, and the outer side of the damaged pile is sleeved with a steel sleeve; fine stone concrete is poured between the steel sleeve and the damaged pile, and a working platform is installed by using the steelsleeve; two ends of the working platform support jacks to reversely jack a cross cover beam, and a micro-expansive grouting material is poured into the gap section between the top surface of a length-jointing pile of the steel sleeve and the bottom of the cross cover beam; and a steel pipe pile is added near the damaged pile, the cross cover beam is lengthened, and the cross cover beam is connected with the steel pipe pile. The cross cover beam is reversely jacked with a jack device to reduce cumulative stress of an upper structure caused by damage, the structural safety stock is not reduced,and the initial stress state of the structural design is restored; and in the process of repairing the damaged pile, the hollow part of the damaged pile is filled with the concrete for reinforcement,the damaged pile is sleeved with the steel sleeve, and the hollow part of the damaged pile is filled with the concrete for strengthening a pile foundation.