Interactions between surface plasmons (SP) of metallic surfaces and photoluminescence (PL) of semiconductor nanocrystal (S-NC) surfaces have been extensively investigated, and SP-induced PL enhancement has been used as a sensitive analytical technique. However, this SP induced electrochemiluminescence (ECL) enhancement is rarely studied. In this work, we report greatly enhanced ECL of CdS thin films by gold nanoparticles (Au NPs) for ultrasensitive detection of thrombin. The system was composed of a CdS NC film on glassy carbon electrode (GCE) as ECL emitter attached an aptamer of thrombin. Then, ssDNA-AuNP conjugates hybridized with the aptamer to form a separation length of ca. 12 nm between CdS NCs and Au NPs. The system showed 5-fold enhancement of ECL intensity as compared to that without Au NPs, which might be attributed to the long-distance interaction between the S-NCs and SPR field of noble metal nanoparticles (MNPs).We also found that the enhanced ECL could be influenced by the involving factors such as the separation distance, spectral overlap, and magnetic field. Such enhancement in combination with smart recognition of aptamer and target protein allowed us to construct an ultrasensitive aptasensor for attomolar detection of thrombin. The presence of target protein was reflected by the ECL signal decrease caused by the target-induced removal of ssDNA-AuNP conjugates. The decrease of ECL signal was logarithmically linear with the concentration of thrombin in a wide range from 100 aM to 100 fM. The principle described in this work could be also applied to many other bioassays.