Abstract: Analyzed here in the essay are the effects on determination of the roll nominal diameter of the steel piperolling mill by the process design,the equipment performance and the production economy.It is regarded via the analysis that determination of the said nominal diameter is influenced by various comprehensive factors;and that sufficientlylarge nominal diameter of the roll of the pipe-rolling mill will assure of the bite conditions,the wall thickness accuracy,and the strength and rigidity of the roll proper;and given the above mentioned conditions are all met,and meanwhile certain heavy load is considered,the roll nominal diameter needs to be as small as possible so as to reduce the production energy consumption,and ensure the stability of the rolling process.