Abstract: Based on a large scale test facility which adopting the SA508Ⅲ steel as heating surface material and utilizing the chemical solution with addition of boric acid（BA:H₃BO₅） or/and trisodium phosphate（TSP: Na₃PO₄） as coolant, the CHF characteristics of chemical solution boiling on a downward facing curved real reactor pressure vessel material surface were investigated experimentally. Experimental results indicate that the CHF values show different changes in different chemical solution environment for the SA508 III steel material. The CHF of BA decreases with the concentration of 1000 to 3000 mg/L and is lower than that of deionized water. The CHF of TSP with lower concentration of 500 and 1000mg/L is enhanced, while weakened for a high concentration of 3500 mg/L. The CHF of mixed solution of BA and TSP increases firstly and then decreases with the increasing of TSP concentration.