Tellurite glasses doping the same concentration of Er3+ were prepared by conventional melting procedure, and their upconversion luminescences were measured. Two green emission bands at 521 nm and 550 nm and one red emission band at 657 nm were observed. This paper reported on the deduction of coordinate field index, which was proposed by deducing from Pauling's rules on the basis of Zachaiasen's random network theory, it was defined to the qualitative index that stand for the deviation of a given truly coordinate polyhedron from the hypothetical one. It can be used to rationalize the remarkable and regularity variation in the upconversion intensity in our prepared tellurite glasses.