The polymerization of ethylene (E) was carried out using a $MgCl_2$-supported $TiCl_4$ catalyst in conjunction with triethylaluminium as a cocatalyst. The effects of the polymerization temperature ($T_p$) and E pressure ($P_E$) on E polymerization were studied. The maximum catalyst activity was obtained at $40^{circ}C$. The melting temperature ($T_m$) and crystallinity ($X_c$) were less affected by the $T_p$. The molecular weight decreased with increasing $T_p$ but the polydispersity index (PDI) increased. In addition, the effect of two stepwise $T_p$ on E polymerization was investigated and the bimodal gel permeation chromatography (GPC) curve was obtained. The catalyst activity increased drastically with increasing $P_E$. The higher $P_E$ in the range of $1-12kgf/cm^2$ showed a higher $M_v$ of the ultra high molecular weight polyethylene (UHMWPE) obtained, whereas increasing $P_E$ decreased the PDI. Because it was very difficult to obtain the molecular weight distribution of UHMWPE through GPC analysis, the molecular weight distribution was analyzed from rheometry measurements of the UHMWPE melt.