The invention relates to a positioning pin assembly device of a printed circuit board, which comprises a casing, a hollow thimble sleeve, a thimble, a guide positioning cylinder and a positioning pin identifying device, wherein the casing is provided with a pneumatic cylinder; the thimble sleeve is connected with the pneumatic cylinder and is positioned into an outer tube, and the thimble sleeve is internally provided with a magnetic attracting element; the thimble is fixed on the thimble sleeve by being attracted by the magnetic attracting element; the guide positioning cylinder is sleeved below the thimble sleeve to surround and cover the thimble, and the bottom end of the guide positioning cylinder is provided with a pin outlet aligned with the thimble; and the positioning pin identifying device is arranged on the casing and is connected with the guide positioning cylinder so as to judge whether the guide positioning cylinder is internally provided with a positioning pin or not. Theinvention can avoid thimble deflection caused by the traditional thread occlusion structure through the magnetic attracting element, and improves the accuracy of the positioning pin assembly.