The nano-scale strain fields analysis around 90° domains and misfit dislocations in PbTiO3/SrTiO3 001 epitaxial thin film has been conducted using the geometric phase analysis (GPA) combined with high angle annular dark field - scanning transmission electron microscopy (HAADF-STEM). The films typically possess a-c mixed domain configuration with misfit dislocations. The PbTiO3 layer was formed from the two layer the upper 200 nm layer shows the typical a- and c- mixed domain configuration where the a-domains are several tens nm in width; the bottom 100 nm layer shows the different domain configuration that the width is several nm. In the latter case, a-domains are terminated within the film and are short in length. On the other hand, the bottom of a-domains does not contact the film/substrate interface. It keeps away from the interface, and there is completely c-domain layer under a-domains. The HAADF-STEM-GPA shows that the strain fields around an a-domain and a misfit dislocation interact each other, the tensile strain field and lattice plane bending fit together. This result infers that the a-domain originates from the misfit dislocation.