Di-tert-butyl peroxide (DTBP) was used as the initiator of polypropylene (PP) degradation, and cobalt stearate and zinc stearate were selected as the additives to catalyze the decomposition of peroxide. The effects of additives on PP degradation was discussed. The results show that with the increase of DTBP content, the melt flow rate (MFR) of PP increases obviously, the mechanical properties decreases, and the crystallization properties improves. When the initiator content increases to 0.6%~0.8%, the melting curve shows two peaks, and the viscosity and modulus decreases. When cobalt stearate is added, the impact property is decreased by 34.63%, the viscosity and modulus decreases, and the MFR of PP further increases. The highest MFR is 59.08% higher than that of the sample without additive, and the crystallization property is higher than that of the sample without additive, and the crystal arrangement is more regular. When zinc stearate is added, the impact property decreases, and the viscosity and modulus decrease. The highest MFR is 200.99% higher than that of the sample without additive, and the crystal arrangement is the most regular. Therefore, zinc stearate is more suitable as an additive for chemical degradation of PP.