Co-vulcanized ethylene-propylene-diene monomer/chloroprene (EPDM/CR) flame retardant rubber was prepared by one step compression molding. The relationship of vulcanization rate, crosslink density and molecular chain mobility, compatibility of EPDM phase and CR phase with mechanical properties and morphology of blends were studied by rotorless rheometer, DMA and SEM. The results show that changing the contents of accelerator ethylene thiourea (ETU∶Na-22) and tetramethyl thiuram disulfide (TMTD), the differences of vulcanization rate and crosslinking density between EPDM and CR phases are effectively reduced, that can improve the co-vulcanization and compatibility of two-phase. By changing the content of compatibilizer maleic anhydride grafted ethylene-propylene-diene monomer (EPDM-g-MAH), the compatibility of EPDM and CR phases is effectively improved, but the vulcanization rate and crosslinking density of EPDM/CR are reduced. When the content of Na-22, TMTD and EPDM-g-MAH is 1.50 phr, 2.10 phr and 10.00 phr respectively, the mechanical properties of EPDM/CR vulcanizate are optimized, especially the tensile strength is 17.84 MPa, the elongation at break is 483.75% and the tearing strength is 28.38 kN/m.