The physic-chemical properties,safety properties,combustion properties and inner ballistic properties of composite modified double-based propellant containing hexanitrohexaazaisowurtzitane(CL-20) (CL-20/CMDB) propellants were studied. Results show that the burning rate of CL-20/CMDB propellant is 2.5～8.94 mm·s^-1 higher than that of RDX/CMDB propellant at 6～20 MPa. The pressure exponent of CL-20/CMDB propellant is greater,which is up to 0.28 at 10～20 MPa. CL-20/CMDB propellant has higher density,explosion heat and specific volume than that of RDX/CMDB propellant. The density,explosion heat and specific volume of CL-20/CMDB propellant is 1.76 g·cm^-3,5034 J·g^-1 and 658 L·kg^-1,respectively. CL-20/CMDB propellant has the same chemical stability as RDX/CMDB propellant,lower impact sensitivity than RDX/CMDB propellant,but higher friction sensitivity,up to 100%； the specific impulse of CL-20/CMDB propellant can achieve 2226.1 N·s·kg^-1(227 s) in Φ36 rocket motor.