Connected and autonomous vehicles (CAVs) have the potential to decrease air pollutants like carbon dioxide, nitrogen oxides (NOx), and sulfur oxides (SOx) through many advanced CAV technologies such as improved fuel efficiency, better routing, and better lane changing. However, CAVs also have the other negative side to increase fuel consumption through electricity spent and negative effects such as longer travel time, and frequent acceleration for comfortable driving. This paper analyses fuel consumption effects of CAV by collecting data from a simulation within cooperative adaptive cruise control (CACC). Compared with normal vehicles (NVs), this paper found that it has significant differences between results of CAVs and NVs. though electricity spent and longer distance time can be damaged, average fuel efficiency and reduced gas emission of CAV technologies far outweigh the disadvantages of those. This paper will help to evaluate various environmental effects on CAV technologies.