Both steel fibers and polypropylene fibers were used to reinforce self compacting lightweight concrete(SCLC). One non fiber SCLC mixtures and four fiber reinforced SCLC mixtures were prepared to conduct the test of rheological properties, mechanical properties and microstructure of SCLC. The fiber reinforcement mechanism in SCLC was investigated on both macro and micro scales. The results show that all five mixtures satisfy the limitations of self compacting concrete that with good flowability, viscosity and passing ability. Steel and polypropylene fibers are effective in arresting cracks at different levels, generating a positive synergistic response, hence, splitting tensile and flexural strengths of SCLC are significantly improved. The microstructure of aggregate paste interface becomes denser with the increase in curing time. There are micro pores between fiber and matrix due to the existence of micro cracks and relatively loose structure.