Abstract: A renewable energy cycle system and method thereof is disclosed, wherein the renewable energy cycle system comprises a water softening equipment, an electrolysis hydrogen equipment, at least a combustion boiler equipment, a generator and at least a steam efficacy conversion device. Herein softened water can be electrolyzed into hydrogen and oxygen by means of the electrolysis hydrogen equipment, and the decomposed hydrogen can be transported to the combustion boiler equipment for combustion such that the liquid in the combustion boiler equipment boils and generates saturated vapor pressure. Next, the generated saturated vapor pressure can be outputted into the steam efficacy conversion equipment such that the steam efficacy conversion equipment can convert the steam efficacy into mechanical energy thereby allowing the steam engine in the steam efficacy conversion equipment to rotate in high speed.