Pr3+,　Yb3+　co-doped　YPO4　downconversion　phosphor　powders　were　prepared　by　solid　state　reaction.　When　excitation　at　450　nm,　the　effects　of　different　Yb3+　mole　fractions　(0%,　1%,　2%,　4%,　20%,　30%)　on　the　conversion　efficiency　are　studied.　Results　shows　that　because　of　the　difference　of　energy　transfer　efficiency　between　Pr3+　and　Yb3+,　the　samples　with　various　Yb3+　doping　concentrations　have　different　fluorescence　intensity.　It　is　also　found　that　the　energy　transfer　process　of　the　downconversion　luminescence　in　samples　is　Pr3+:　3P0→Yb3+:　2F5/2+2F5/2.　From　photoluminescence　spectra　measurement,　the　optimal　doping　mole　fraction　of　Yb3+　is　2%.　The　results　indicate　that　Pr3+,　Yb3+　co-doped　YPO4　downconversion　phosphor　is　a　kind　of　potential　material　which　may　be　used　to　improve　the　solar　cell　efficiency.