The demand of compactness and light-weight for thermoelectric applications requires optimized system integration of thermoelectric module and heat sinks to achieve the best performance under size and weight constraints. This work studies the thermal resistance matching (i.e., optimal thermal resistance allocation of thermoelectric module and heat sinks) for real thermoelectric cooling systems via an integrated theoretical and experimental method. A theoretical model is first developed to study the relationship of thermal resistance allocation and the system cooling power under different operating currents. Modeling results indicate that the optimal thermal resistance of thermoelectric module should account for 40-70% of the total thermal resistance. The effectiveness of thermal resistance matching is then demonstrated in the selection of an optimal thermoelectric module among 73 off-the-shelf modules to develop a portable thermoelectric cooling system. By comparing the cooling performance of two thermoelectric cooling systems with and without thermal resistance matching, it is experimentally demonstrated that the system with thermal resistance matching achieved 10.7-19.8% larger cooling power under the same size and weight constraints. This can be used as a guideline for optimal design of thermoelectric cooling systems.