The invention relates to an in-situ repairing method of upper pinner of a rail transit bridge support and a pinner formwork. The method includes the steps of installing a first temporary support between the bottom of a main beam and a cover beam, installing a temporary supporting column on the outermost side of the main beam, installing a second temporary support on the temporary supporting column, supporting the weight of the main beam through jacks on the first temporary support and the second temporary support, removing defective concrete on the upper pinner, installing a steel fabric and erecting the pinner formwork at the to-be-repaired position of the upper pinner, pouring slurry into a cavity defined by the erected pinner formwork, monitoring the solidification time of slurry, controlling the jacks of the temporary support to relieve pressure after it is determined that the solidification time of the slurry reaches a preset time threshold value so that the upper surface of the repaired pinner can be closely attached to the bottom of the main beam. Construction is quite easy and convenient, only the weight of the bearing main beam needs to be changed through dragging, the large displacement of the main beam is not needed, the supports do not need to be detached or replaced, and therefore the method is short in construction time, low in expense and little in influence on existing lines.