Thermal or cold storage is a promising way to alleviate the peak-valley difference of the electricity load and improve the energy efficiency. The thermal or cold storage by micro-encapsulated phase change material (MPCM) slurry is one of the effective measures to be implemented in waste heat recovery and heat transport system etc. due to its high energy storage density and excellent heat transfer performance. The thermo-fluidic performances of the MPCM slurry flowing through the horizontally circular pipe under constant heat flux are numerically investigated based on the Eulerian-Eulerlan approach in the present study. It is found that the numerical results are in good consistence with the experimental results from the aspects of flow and heat transfer. The influences of particle diameter on solid volume fraction distribution, solid velocity distribution and pressure drop of the MPCM slurry are investigated under isothermal condition. And then the temperature distribution of the MPCM slurry and liquid volume fraction of the PCM in MPCM are presented to analyze the heat transfer performance of the MPCM slurry. The particle diameter also imposes significant influences on the heat transfer between the two phases and average heat transfer coefficient of the MPCM slurry. The largest pressure drop and the highest average heat transfer coefficient appear when the particle diameter of the MPCM decreases to 1 jun. Further investigations at different Reynolds numbers are carried out to study the variation of local heat transfer coefficient along the pipe. Finally, the comparison of energy transport performances between the MPCM slurry and water are presented based on the ratio of transported heat to pumping power. The MPCM slurry shows better energy transport performance than pure water when the Reynolds number is above 7865.