The utility model relates to a device which is used for adjusting material concentration. The utility model discloses a method of two-step crystal zone method for adjusting the solution concentration of the diphenol propane and provides a simple, low cost and in time device for adjusting the solution concentration of the diphenol propane in two-step crystal zone method. The definite method is that arrange a solution circulation loop through the solution which is formed by dissolving adducts of phenol and diphenol propane which is deposited by primary crystallization and centrifugation with the phenol, and get the concentration by detecting the crystal temperature of the solution which is on the circulation loop. The utility model also discloses a device in that a bye-pass exit is arranged between the material out pump and the second crystal feeding valve. A crystal temperature detecting control valve is arranged between the bye-pass exit and the crystal chamber. The material outlet of the crystal chamber is connected with the material inlet of the diphenol propane solution which is on the dissolve kettle. Due to that the material concentration has good corresponding relation with the crystal temperature, the method has the advantages of accurate and fast measurment.