By polymerization of gadolinium methacrylate (Gd (MAA)3), lead methacrylate (Pb(MAA)2) and methylmethacrylate (MMA), Gd and Pb were chemically bonded into polymers. The X-ray shielding performance was evaluated by Monte Carlo simulation method, and the results showed that the more metalfunctional organic monomer, the better the shielding performance of terpolymers. When the X-rayenergy is 65 keV, Gd (MAA)3-containing polymers have better shielding performance than Pb(MAA)2-containing polymers. Gd could compensate for the weak absorption region of Pb. Therefore, polymerscontaining both Gd and Pb enhanced shielding efficiency against X-ray in various low-energy ranges. Forobtaining terpolymers with uniform monomer compositions, the relationship between the monomercomposition of the terpolymers and the conversion level was optimized by calculating the reactivityratios. The value of reactivity ratios of r (Gd (MAA)3/Pb(MAA)2), r (Pb(MAA)2/Gd (MAA)3), r (Gd (MAA)3/MMA), r (MMA/Gd (MAA)3), r (Pb(MAA)2/MMA) and r (MMA/Pb(MAA)2) was 0.483, 0.004, 0.338, 2.508,0.255, 0.029. The terpolymers with uniform monomer composition could be obtained by controlling themonomer compositions or conversion levels. The results can provide new radiation protection materialsand contribute to the improvement in nuclear safety.