The neutron diffraction results obtained by oscillating and fixing during data collection show that the high ageing temperature is effective to eliminate dendrite crystals and the microstrain exists mainly in the ' phase. Based on the microstructure obtained by neutron diffraction and scanning electron microscope, the influence of ageing temperature and time on ' phase are evaluated. The unique misorientations among ' phase grains are observed from superlattice measurements. According to the neutron diffractions of different crystal planes, the crystal symmetry is slightly changed from cubic to quartet (a c) due mainly to the matrix phase and the experimental results also prove the strain deviation in difference orientations, thus providing the basis for the existence of driving force for the raft model. The calculation based on the superlattice diffraction shows that in the interfaces between the and ' phases exists a complex distortion: the mismatch varies from -0.1% to -0.3% and the mismatch value can be reduced by high temperature during the first ageing and long time during the second ageing.