The invention discloses a production method of solid orthophosphoric acid, comprising the following steps: adding wet phosphoric acid or thermal phosphoric acid with the mass percent concentration of 70-85% into a concentrating device, heating to 130-262 DEG C at a speed of 4 DEG C per minute, concentrating for 1-2h under ordinary pressure to negative 0.085 MPa to obtain the dehydrated phosphoric acid solution with the mass percent concentration higher than 99%, placing the dehydrated phosphoric acid solution with the mass percent concentration higher than 99% into a reactor, the temperature of which is controllable, adding hydrogen peroxide by amount of 0.1-0.8% of the raw material acid, reacting for 8-30min at the temperature of 60-130 DEG C while stirring the mixture, cooling the reaction product to 10-28 DEG C, and adding orthophosphoric acid seed crystal to obtain the solid orthophosphoric acid. For the invention, the technique is simple and easy for industrialization, production cost is low, productivity is high, the technique is characterized by having no return product, and the product is convenient in packaging and transporting.