The present invention discloses polyethylene powder, a composition, a cross-linked polyethylene pipe and preparation methods of the polyethylene powder and the cross-linked polyethylene pipe. The polyethylene powder preparation method comprises that under the co-effect of a supported non-metallocene olefin polymerization catalyst and a co-catalyst, in the presence or absence of hydrogen, ethylene and alpha-olefin are subjected to slurry polymerization in an organic solvent, wherein the co-catalyst is one or a plurality of materials slected from an alkyl aluminum compound, a halogenated alkyl aluminum compound and alkyl aluminoxane. According to the present invention, the cross-linking degree of the obtained cross-linked polyethylene pipe can achieve more than or equal to 90%, the compression resistance can achieve and exceed the national standard related requirements, and the test results through the experiment examples show that the polyethylene powder prepared of the present invention has good environmental stress cracking resistance compared to the ethylene copolymer raw material prepared by using the existing technology.