A method for compensating for a signal error at a transmit end of an optical time domain reflectometer is provided. The method includes: detecting an actual signal sequence of a PN sequence sent by a transmitter to a measured optical fiber and an actual signal sequence of an optical signal and reflected back by the measured optical fiber and received by a receiver (101); obtaining, through computation and according to the actual signal sequence of the PN sequence, a theoretical signal sequence of the PN sequence, and an optical fiber attenuation curve function obtained through an adjacent previous iterative computation, a compensation value of the optical signal that attenuates in a process in which the optical signal is reflected by the measured optical fiber (102); computing, according to the actual signal sequence of the optical signal, the compensation value, and the theoretical signal sequence of the PN sequence, an optical fiber attenuation curve function obtained through a current iteration (103); and determining, when determining that the optical fiber attenuation curve function obtained through the current iteration satisfies a given condition, performance of the measured optical fiber according to the optical fiber attenuation curve function obtained through the current iteration (104). Further, an apparatus for compensating for a signal error at a transmit end of an optical time domain reflectometer is provided.