A derivation of an analytical expression for the inviscid velocity field induced by a single right-handed helical vortex filament is presented. The vortex filament moves uniformly and rigidly without change of form in a cylindrical tube, where the vortex filament rotates around its axis with a constant angular velocity and translates along its axis with a constant translational velocity. The key to solve the problem is to set up a moving cylindrical coordinate system fixed on the vortex filament. The result shows that the velocity field is a time-periodic function, and may degenerate into Okulovs’s formula when the helical vortex filament slips along the filament itself or stays immobile.