This paper, taking environmental regulation intensity as threshold variable, uses threshold model to study the impact of two-way FDI on China's carbon emission in order to check if there is carbon pollution paradise effect from IFDI（inward foreign direct investment） and OFDI（outward foreign direct investment） under different environmental regulation intensities. The result is no. IFDI plays a key role in carbon emission in China varying with environmental regulation intensities; carbon emission will reduce as environmental regulation intensities tighten. OFDI's impact on carbon emission shows an upside-down U shape that carbon emission will soar if OFDI expands when environmental regulation intensities descend, and that carbon emission will be restrained when environmental regulation intensities tighten. Among carbon emission reduction effects from technical overflow, IFDI exceeds OFDI in that China is at the initial stage of OFDI, but at middle to late stage of actual use of IFDI.