A series of soluble methyl-containing polyimides (MPI) were prepared by a one-step high-temperature copolymerization using 2,6-diaminotoluene(TDA), 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride(ODPA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride(BPDA) as monomers and m-cresol as the solvent. Their structures and properties were tested by FTIR, 1HNMR, DSC, TGA, UV, etc. The series of methyl-containing polyimides had good solubility in NMP, DMAc, DMSO, DMF, CH2Cl2 and CHCl3 at room temperature, and their solubility decreased as increasing of the content of biphenyl anhydride. The obtained films showed good optical transmission properties, and the transmittance at the ultraviolet light wavelength of 450 nm was above 74%, and the cutoff wavelengths were around 350 nm. The series of polyimides also had good thermal properties. The initial decomposition temperatures of this series of MPI were more than 457 °C, and their glass transition temperatures were in the range of 260 °C~285 °C. The elastic modulus, tensile strength and elongation at break of the prepared films were in the range of 1.7~2.1 GPa, 89.7~120.6 MPa and 19.7%~28.4%, respectively.