The present study investigated the underlying cognitive and neural mechanisms of object code switching in sentence contexts from Chinese to English (L1-L2) and from English to Chinese (L2-L1) for Chinese learners of English. ERP data analyses indicated that (1) code switched English objects produced significantly larger P200 and N400 than non-code switched English objects did; (2) code switched Chinese objects elicited significantly larger LAN and LPC than non-code switched Chinese objects did; (3) the asymmetry of switching cost from Chinese to English and from English to Chinese existed in larger P200, LAN and LPC for code switching from English to Chinese. We concluded that there existed intra-sentential code switching effects and corresponding asymmetry of switching costs for Chinese learners of English in terms of objects at sentence level, and the models for code switching effects and asymmetry of switching costs are tentatively built based on IC Model and BIA+ Model to provide a better explanation for the results.