The invention relates to a high-precision vertical downward insertion construction device and method for a steel vertical column. The device comprises upper and lower clamping assemblies used for clamping the steel vertical column and an adjusting assembly used for adjusting the relative positions of the upper and lower clamping assemblies. The construction method comprises the following steps that step 1, the steel vertical column passes through first and second through holes of the upper and lower clamping assemblies; step 2, a first clamping part clamps the steel vertical column, a second clamping part loosens the steel vertical column, the verticality of the steel vertical column is adjusted by adjusting an upper clamping assembly through a rotating mechanism, and a linear motion mechanism drives the upper clamping assembly to move downward for a certain distance to drive the downward insertion of the steel vertical column; step 3, the second clamping part clamps the steel verticalcolumn, the first clamping part loosens, the linear motion mechanism drives the upper clamping assembly to rise, and step 2 to step 3 are repeated for one time or above until the downward insertion of the steel vertical column reaches a designed depth. The construction device and method can adjust the verticality of the steel vertical column with multiple degrees of freedom, and improve the precision of the downward insertion construction.