A series of YLiF4: Er3+ , Tm3+ , Yb3+ samples were synthesized by hydrothermal method. The concentrations of Er+ and Yb3+ were 1 mol% and 1.5 mol%, respectively. Tm3+ concentration changed from 2 to 8 mol%. The absorption of Er3+, Tm3+ and Yb3+ were observed, and the absorption of Tm3+ increased along with the increase in Tm3+ concentration. The color of upconversion luminescence of YLiF4: Er3+, Tm3+ and Yb3+ excited by 980 nm was white when Tm3+ concentration was low. The blue light resulted from the transition of 1G4-->3H6 of Tm3+, the green light from the transition of 4S(3/2)(2H(11/2))-->4I(15/2) of Er3+, and the red light from the transitions 1G4-->3F4 of Tm3+ and 4F(9/2)-->4I(15/2) of Er3+. All the upconversion intensities decreased when Tm3+ concentration increased, but the relative intensity decrease was different due to the interaction between Er3+ and Tm3+.