In nanopharmaceutics, a robust manipulation of the preparation process and an accurate prediction of the final product size are very important for developing novel nano drug delivery systems. In the present study, for the first time, a process parameter, i.e. the length of the straight fluid jet, L, is correlated with an experimental parameter, i.e. fluid flow rate, F; a nanofiber property, i.e. diameter, D; and the corresponding drug-sustained release profile. Using a mixed solution consisting of 15% (w/v) polyacrylonitrile and 3% (w/v) ketoprofen in acetone and N,N-dimethylformamide (2:8, v:v) as a spinnable working fluid, a series of medicated nanofibers were prepared under variable F and were characterized. The analysis results disclosed the quantitative relationships among different types of parameters. The process parameter L exhibited a better linear relationship with the nanofibers’ diameter (D) than the processing parameter F. These results give a hint that process parameters can be exploited as useful tools for accurately predicting and tailoring the resultant nanofibers’ D, and in turn their functional performances. The strategy proposed here presents a new approach to investigate the electrohydrodynamic process and manipulate the functions of nanoproducts through process-property-performance relationships.