Continuous wave mode-locked neodymium phosphate glass laser requires special resonator design since Nd: phosphate glass has low thermal conductivity and damage threshold. We analyze the characteristics of a three-element resonator under the restraint of a fixed resonator length and discuss the design of the optical resonator for the CW actively mode-locked Nd: phosphate glass laser. We discuss the stability ranges and characteristics of resonator under different parameter regions and illustrate the best parameter region of interest. Analytical expressions of resonator parameters for optimum operation regime are given. The experimental results agree well with theoretical predictions. This analysis may be useful for the design of any end-pumped and mode-locked resonator with three elements or more elements.