The invention provides a method for improving crystallinity of polyacrylonitrile nascent fibers. The method comprises steps as follows: polymerizing acrylonitrile and comonomer free radicals to obtain an acrylonitrile polymer solution, obtaining a spinning solution through demonomerisation and deaeration, then controlling the channel temperature and the flow rate of the spinning solution at a spinneret orifice to obtain a spinning trickle with the viscosity eta ranging from 500 P to 700 P, and obtaining the nascent fibers through spraying by a spinneret plate, consolidation forming and drying. The crystallinity of the nascent fibers prepared with method is higher than 49% and higher than that of nascent fibers obtained under equal conditions with different eta values.