In this paper, fractal dimensions of fractional calculus of continuous functions defined on [0, 1] have been explored. Continuous functions with Box dimension one have been divided into five categories. They are continuous functions with bounded variation, continuous functions with at most finite unbounded variation points, one-dimensional continuous functions with infinite but countable unbounded variation points, one-dimensional continuous functions with uncountable but zero measure unbounded variation points and one-dimensional continuous functions with uncountable and non-zero measure unbounded variation points. Box dimension of Riemann-Liouville fractional integral of any one-dimensional continuous functions has been proved to be with Box dimension one. Continuous functions on [0, 1] are divided as local fractal functions and fractal functions. According to local structure and fractal dimensions, fractal functions are composed of regular fractal functions, irregular fractal functions and singular fractal functions. Based on previous work, upper Box dimension of any continuous functions has been proved to be no less than upper Box dimension of their Riemann Liouville fractional integral. Fractal dimensions of Riemann -Liouville fractional derivative of certain continuous functions have been investigated elementary.