Based on the dynamic model of ethylene slurry polymerization
a decoupling method was proposed for rigorous model calculation of molecular weight distribution(MWD).The MWD model in large scale differential-algebraic equations(DAEs) was decoupled to a moment model in small scale DAEs and chain length based MWD in large scale ordinary differential equations(ODEs).The variable decoupling method was further proposed to solve the large scale ODEs through numerical computation. Comparison of the MWD curves with Flory distribution calculation was also presented and discussed.