Microplastics pollution have been a major concern in the past several decades. More and more research are focusing on the occurrence of microplastics in different environments, which are important to estimate the impact of microplastics to organisms. This study conducted a full factorial exposure experiment with the form (fragment, fibre) and concentration of MPs (10, 100, and 1000 items /L), and exposure duration (2, 4, and 8 days) being independent factors, using acorn barnacle Amphibalanus amphitrite. A. amphitrite can trap and ingest the suspended particles in water and cannot intentionally remove the inedible particle. Most previous studies used microplastic beads for experiments, which are regular in shape and usually commercially available. This study used microplastic fibres (63-250 micrometer) and fragments (65-125 micrometer) for the exposure experiments, which are more similar to the true situation in marine environment. The results indicated that the abundance of microplastics in barnacles are positively related to the concentration of microplastics in the environment, and there is not difference between microplastics of different shapes. The abundance of microplastics in barnacles accumulate to maximum after 4 days exposure and there is no further increase after that. This study further proved that A. amphitrite can be a bioindicator for microplastic pollution in marine coastal environment, providing a new method for microplastic monitoring.