High field dipole magnets with common-coil configuration are under development at IHEP (the Institute of High Energy Physics, Chinese Academy of Sciences) for key technology pre-study of high energy colliders like SPPC (Super Proton-Proton Collider). A model magnet named LPF1 has been fabricated and tested in 2018, which was made up of 4 flat racetrack NbTi coils and 2 flat racetrack Nb3Sn coils, and a main dipole field of 10.2 T has been reached in the two apertures at 4.2 K. A new model magnet LPF2 is being designed and fabricated in 2019, with 4 new Nb3Sn coils included comparing with LPF1, and the magnet is expected to reach a much higher field. To reduce the field enhancement at the coil ends, the new fabricated Nb3Sn coils are designed with different straight lengths and bending radiuses. This hybrid dipole magnet is designed to provide a 12-T main field in the up and bottom apertures with an operating current of 5300 A, corresponding to a load line ratio of 78 % at 4.2 K. A single-pancake racetrack IBS (Iron-based superconducting) coil wound with a 100-m IBS tape is inserted into the middle of the magnet. This magnet is also used to test the IBS coil performance under high field and high stress. The main design parameters, fabrication process and the test results of the magnet will be presented.