Structures and crystal form transition of the novel aryl ether ketone polymer containing meta-phenylene linkage:PEKEKK(T/I) were investigated by wide angle X-ray diffraction (WAXD), imaging plates (IPs) and small angle X-ray scattering (SAXS). The energy of activation of the decomposition reaction and degree of crystallinity of PEKEKK(T/I) were determined by WAXD and thermo-gravimetric analysis (TGA), respectively. Results obtained from WAXD and IPs show that crystal forms Ⅰ and Ⅱ coexist in the PEKEKK(T/I) samples isothermally cold crystallized in the temperature range from 180℃ to 240℃ and only form I occurs in PEKEKK(T/I) samples isothermally cold crystallized at 270℃. The radius of gyration (Rg), thickness of microregions with electron-density fluctuations (E) and distribution of particle sizes were investigated by SAXS.