The invention provides a method and a device for optimizing dynamic transmission performance in a wavelength switched optical network. The method comprises the following steps of: making the optical signal-to-noise ratio cost of a dispersion-optimized optical path and the accumulative nonlinear phase shift have a one-to-one correspondence relationship by carrying out pre-dispersion compensation and post-dispersion compensation on source and destination nodes of an optical path; then, obtaining the optical signal-to-noise ratio cost of the optical path, using the power regulating quantity of apower-regulating point as a variable, by using the correspondence relationship, further setting a target function according to the optical signal-to-noise ratio cost and the optical signal-to-noise ratio of the optical path, and optimizing according to a predetermined optimization target and constraint conditions to obtain a node needing power regulation and the power regulating quantity of the same. According to the invention, the transmission performance of the optical path can be improved, and the blockage of physical layers, caused by the substandard physical transmission performance, is avoided.