Direction: perpendicular to the paper.

Description: The magnetic field at O is composed of two semi-infinite current-carrying straight wires and a current-carrying circular coil * *, and the two semi-infinite current-carrying straight wires can be equivalent to one infinite current-carrying straight wire. The total magnetic field at point O can be obtained by adding the magnetic field formulas of the current-carrying circular coil and the infinite current-carrying straight wire, but the magnetic field generated by the infinite current-carrying straight wire at point O is perpendicular to the paper surface, while the magnetic field generated by the current-carrying circular coil at point O is perpendicular to the paper surface. So it's a subtraction relationship. Obviously, the magnetic field generated by the current-carrying circular coil at point O is greater than that generated by the infinite current-carrying straight wire at point O, so the total magnetic field direction is the same as that generated by the current-carrying circular coil at point O, and both are perpendicular to the paper.