Based on the particular requirements in IR46 about protection of metrological properties, and combined with the design idea of dure-core smart meter issued by domestic researchers, a novel smart meter software realization scheme based on data flow and modularity is proposed, aiming to improve the software reliability. And also, using minute energy as its core data, a new calculation method of electrical energy and demand is proposed and its process flow is redesigned. With the design frames above, a safe and reliable software update method is proposed, in which updating procedure does not influence metering functions. At last, combined with the software characteristics of smart meter, some software reliability test methods including software acceleration and fault injection are proposed. These design and test methods effectively guarantee the software reliability of the novel smart meter based on IR46.