Abstract: The main Cooling Storage Ring (CSRm) of HIRFL-CSR is used to accumulate, accelerate and extract the charged ion beam to experimental terminal. During accumulation in CSRm, the Multiple Multiturn Injection method with electron cooling is applied at the injection energy to increase beam intensity. Theoretical analysis suggests that the cooling rate and beam lifetime have a strong influence on the beam intensity. On the one hand, electron cooling can quickly shrink the size, divergence and the momentum spread of stored ion beams, which is also used to reduce beam loss caused by Intra Beam Scattering (IBS). On the other hand, the recombination effects between electrons and ions will result in the beam loss. Some experiments on C6+ beam and Ar15+ beam were carried out in CSRm to investigate the relationship between electron cooling and beam lifetime. The beam lifetime was remarkably increased when electron cooling was applied. The effects of the electron beam parameters (density, current, energy and expansion factor) on the ion beam lifetime were measured. The results of the measurement were analyzed based on the electron cooling and recombination theory, and how the electron cooling affect the beam lifetime was studied. According to the measurement results and the analysis, the electron beam parameters were optimized to increase the beam lifetime and the ion beam intensity could be increased to a high level accordingly.