The invention discloses a phase information obtaining method and system, and a magnetic resonance imaging system. The method comprises: phase values of all receiving channels at a first frequency and phase values of all the receiving channels at a second frequency are measured; for each receiving channel, a phase difference between the phase value of the receiving channel at the first frequency and the phase value of the receiving channel at the second frequency is calculated; and for any receiving channel, calculation is carried out to obtain a phase value of the receiving channel at a target frequency according to the phase difference of the receiving channel, a corresponding phase difference of a reference channel, a frequency difference between the first frequency and the second frequency, the target frequency, and a determined phase value of the reference channel at the target frequency. Therefore, the measurement efficiency and the measurement accuracy of phase information can be improved.