Summary: Here, it is considered that constant failure rates of the components are fuzzy in nature. The failure rate of components is taken as a triangular fuzzy number. The reliability function of system reliability is expressed in terms of fuzzy numbers of the components reliability. Simple reliability models are taken in fuzzy environment and then its reliability is evaluated. Fuzzy system reliability of series systems, parallel systems, $k$-out-of-$n$ systems and cold standby systems are approximated. Then, the corresponding left and right divergences are computed, which are occurring due to approximation of system reliability. Numerical examples are given to illustrate the approaches.