Using a one-dimensional positron annihilation angular correlation spectromter （FWHM= 0.33mrad） and a positron lifetime spectrometer （FWHM=0.305ns）

we have performed the measurements on angular correlation and positron lifetime spectra of the gamma rays produced by positron annihilation in a series of melt-crystalline polyethylene with different crystallinities and those irradiated by 60Co with different doses. The relation between molecular structure and positron annihilation parameters is discussed.