Different routes for preparing poly(aryl ether ketone)s (PEKKs) are presented and compared. The properties of PEKKs are related to the content of metaphenyl links in the molecular main chains, the molecular chain branching degree, the gelation content by molecular crosslinks, and, especially, the relative content of crystal form II to crystal form I of the PEKK polymorphism. When the molecular T/I ratio of 50/50 in the polymer chains is reached, the obtained PEKK has a lower melting point and gelation content (2% or so). The PEKKs prepared from the electronical substitution route (E route) often have a 0-30% content of crystal form II (relative to the mixed form I and form II), which is much more than that in PEKKs from the nucleophilic substitution route (N route, form II accounts for 0-20%). The relatively unstable crystal form II resulted in the unstable and difficultly predicted thermal properties of PEKKs. PEKKs from different routes provide samples with melting points from 360 to 397 degrees C (T-m) and glassy transition temperatures (T-g) from 167 to 176 degrees C and the equilibrium melting point of 411 degrees C for para-PEKK, while the tensile strength of the homopolymer PEKK and copolymers of PEEKK (poly(aryl ether ether ketone ketone)-PEKK can reach 100 MPa prepared by the N route. The high T-g makes PEKK polymers practically useful while too high T-m and a very small difference between T-m and T-d (degradation temperature) produce obstacles to its wide application. The reaction mechanisms of both electrophilic and nucleophilic routes are investigated and discussed in detail. Results show that the molecular chain branched by solvents and monomers with many activated points may be partly reduced to some extent by the oligomer and extruding route.