High field superconducting magnets are the key components of Super proton proton Collider (SppC).SppC needs 20-T level accelerator magnets to deflect or focus proton beam.There are four kinds of coil configurations for accelerator magnets: cos-theta type,common coil type,block type and canted cos-theta type.A design study of the 20-T 2-in-1 dipole magnet has been carried out with the cos-theta coil configuration.