An optical add-drop multiplexer, comprising: an optical processing component, a first combining device, a second combining device, and a second scrambler, wherein the optical processing component comprises an input end, a first output end, a second output end, and a third output end; the first combining device comprises a first input end, a second input end, and an output end; and the second combining device comprises a first input end, a second input end, and an output end; the first output end of the optical processing component is connected to the first input end of the second combining device, and the second output end of the optical processing component is connected to an input end of the second scrambler; an output end of the second scrambler is connected to the second input end of the second combining device; and the third output end of the optical processing component is connected to the first input end of the first combining device; and trunk signals comprising an express signal and a drop signal enter the optical processing component from the input end of the optical processing component, and the optical processing component processes the trunk signals into a second drop signal, a first express signal, and a second express signal, wherein the first express signal and the second express signal are the same as the express signal, and the second drop signal is the same as the drop signal; the second drop signal enters the first input end of the second combining device through the first output end of the optical processing component; the first express signal enters the input end of the second scrambler through the second output end of the optical processing component, the second scrambler scrambles the first express signal that enters the input end of the second scrambler, to obtain a scrambled express signal, and the scrambled express signal enters the second input end of the second combining device through the output end of the second scrambler; the second combining device combines the second drop signal that enters the first input end of the second combining device and the scrambled express signal that enters the second input end of the second combining device, and then outputs a second combined signal at the output end of the second combining device; and, the second express signal enters the first input end of the first combining device through the third output end of the optical processing component, and the first combining device combines the second express signal that enters the first input end of the first combining device and an add signal that is from a branch adding port of the optical add-drop multiplexer and enters the second input end of the first combining device, and then outputs a first combined signal at the output end of the first combining device. an optical processing component, a first combining device, a second combining device, and a second scrambler, wherein the optical processing component comprises an input end, a first output end, a second output end, and a third output end; the first combining device comprises a first input end, a second input end, and an output end; and the second combining device comprises a first input end, a second input end, and an output end; the first output end of the optical processing component is connected to the first input end of the second combining device, and the second output end of the optical processing component is connected to an input end of the second scrambler; an output end of the second scrambler is connected to the second input end of the second combining device; and the third output end of the optical processing component is connected to the first input end of the first combining device; and trunk signals comprising an express signal and a drop signal enter the optical processing component from the input end of the optical processing component, and the optical processing component processes the trunk signals into a second drop signal, a first express signal, and a second express signal, wherein the first express signal and the second express signal are the same as the express signal, and the second drop signal is the same as the drop signal; the second drop signal enters the first input end of the second combining device through the first output end of the optical processing component; the first express signal enters the input end of the second scrambler through the second output end of the optical processing component, the second scrambler scrambles the first express signal that enters the input end of the second scrambler, to obtain a scrambled express signal, and the scrambled express signal enters the second input end of the second combining device through the output end of the second scrambler; the second combining device combines the second drop signal that enters the first input end of the second combining device and the scrambled express signal that enters the second input end of the second combining device, and then outputs a second combined signal at the output end of the second combining device; and, the second express signal enters the first input end of the first combining device through the third output end of the optical processing component, and the first combining device combines the second express signal that enters the first input end of the first combining device and an add signal that is from a branch adding port of the optical add-drop multiplexer and enters the second input end of the first combining device, and then outputs a first combined signal at the output end of the first combining device.