In this paper, the capacity titration technique (CT technique) was developed on basis of the RPG (ratio of potentio-charge capacity to galvano-charge capacity) method to continuously determine the solid diffusion coefficient D of the intercalary species within insertion-host materials with a small voltage region. The linear equations of D vs. q (value of ratio of the potentio-charge capacity to the galvano-charge capacity) were given in different range of q. By the CT technique,the Li+ solid diffusion coefficients D within LiMn2O4 at different voltages were determined. The results showed that the values of D varied from 3.447× 10-9 cm2/s to 7.60× 10-11cm2/s in the voltage range of charge from 3.3V to 4.3V as a function of voltage with "W" shape.