The present invention provides an updating apparatus and method for an equalizer coefficient, receiver and optical communication system. The updating method comprises: receiving an optical signal transmitted by a transmitter in an optical communication system, the optical signal comprising transmission data and a constant modulus signal for updating a coefficient of an equalization filter; performing coherent detection and analog-to-digital conversion on the optical signal, so as to obtain a digital electric signal; and updating the coefficient of the equalization filter at a symbol corresponding to the constant modulus signal in the digital electric signal. With the embodiments of the present invention, not only the coefficients of the equalizer may be optimized, but also being adapted to signals in various modulation formats, and the complexity of the channel equalization may be lowered as well.
