Tm3+/Yb3+ codoped lanthanum-zinc-lead-tellurite glasses were prepared. Infrared spectrum and upconversion luminescence spectra under 980 nm excitation were studied, and the upconversion luminescence mechanisms were discussed. Rate equations based on energy levels of Tm3+ and Yb3+ and the upconversion mechanisms were developed, and population density in different levels and coefficients of the energy transfer rate Cbi(i=0, 1,3) between Tm3+ and Yb3+ were obtained. The results indicated that, with increasing PbO content in the glass, the energy transfer between Yb3+:2F5/2 and Tm3+:3H4 was intensified, and upconversion luminescence intensity of blue emission was enhanced significantly.