The invention relates to a manufacturing process of preparing a silicon nitride ceramic circuit board, and belongs to the manufacturing field of electronic components. The manufacturing process is characterized by including the following steps: adding sintering aids into silicon nitride powder proportionally, and evenly stirring to obtain powder; adding the obtained powder into an organic solvent proportionally, and performing grinding and mixing to obtain an evenly-mixed sizing agent with the pH value of 9-10; subjecting the sizing agent to mixed grinding in a planetary ball mill for 22 hours, discharging a product, and subjecting the product to vacuum stirring and degassing under the condition of -0.09Pa for 1 hour to obtain a water-base ceramic sizing agent, wherein solid content of the water-base ceramic sizing agent is 56-58%, flow speed thereof is smaller than 30 seconds, and the water-base ceramic sizing agent does not sediment in 8 hours; producing a ceramic blank strip from the water-base ceramic sizing agent through spraying, drying the ceramic blank strip into a solid blank strip, and cutting the blank strip into a blank sheet; feeding the blank sheet into a sintering furnace to sinter, and cooling the blank sheet to obtain a green body of the silicon nitride ceramic circuit board; putting the green body of the silicon nitride ceramic circuit board in the ball mill for grinding and polishing by 0.5-micrometer silicon nitride dry powder.