The invention relates to a gel spinning solution of polyacrylonitrile-based carbon fiber precursor without skin-core structure, comprising the following ingredients: water or alcohol compound, polyacrylonitrile and organic solvent with mass ratio of 1:1-50:5-150; the preparation method comprises the following steps: water or alcohol compound is dissolved in organic solvent, polyacrylonitrile is added, and then the mixture is stirred and is dispersed uniformly at normal temperature; and then the solution is swelled for 2-6 hours, the temperature is raised to 60-80 DEG C, and then the mixture is stirred continuously, and finally, the mixture is placed still at constant temperature of 60-80 DEG C for 2-10 hours, and then filtration and still defoaming are carried out, so as to prepare the polyacrylonitrile gel spinning solution; the gel spinning solution reduces the gel temperature for gel spinning, simplifies the spinning process, reduces the process cost, has good economic benefit and is suitable for industrial production.