The invention discloses a method for compensating asymmetric line delay caused by OLP (Optical Line Protection) switching, which comprises the following steps of: setting a port of designated OSC (Optical Supervisory Channel) to work in the BC (Boundary Clock) or OC (Over Clock) mode, and enabling the corresponding OLP to have the automatic compensation function on the port; setting an OLP unit to work at asymmetric delay compensation values of different receiving and transmitting lines on an OSC designated port of a site with OLP; receiving the working state of the line and transmitting to the OSC at the same site in the form of switched bytes through a back plate by the OLP unit; and analyzing the received OLP switched bytes of the opposite site by the OSC, combining with the OLP switched bytes of the site, determining the actual working state of the OSC port at the site in the line protection section, and selecting the set corresponding compensation value to compensate on the slaveend. By applying the invention, asymmetric delay caused by OLP switching can be compensated in real time, the compensation effect is unrelated to the OLP section, and the stability of time synchronization during OLP switching is ensured.