To evaluate the key factors of Tianjin's oceanic resources environmental carrying capacity, this paper selects 27 indicators among oceanic resource system, oceanic environmental system and social economy system to establish an evaluation index system of oceanic resources environmental carrying capacity, with entropy-weighted TOPSIS model applied to evaluate Tianjin's oceanic resources environmental carrying capacity during 2007 to 2016 and its three sub-systems, key factors identified with gray correlation coefficient. In the period of 2007 to 2016, Tianjin's oceanic resources environmental carrying capacity amounts to 0.3412 to 0.5664, an intermediate level, showing a developing trend of descending-stabilizing-rising-stabiliing, descending during 2007 to 2010, stabilizing during 2010 to 2012, rising conspicuously during 2012 to 2014, and gradually stabilizing during 2014 to 2016. Tianjin's oceanic resources carrying capacity has a little change, its oceanic environmental carrying capacity shows a “V-shaped” trend and its social economic carrying capacity has a “W-shaped” trend. Gray correlation coefficient calculation indicates that key factors are annual sulfur dioxide and pollution control investment to GDP. This paper presents suggestions on rationally developing oceanic resources and developing coastal tourism aiming at improving Tianjin's oceanic resources environmental carrying capacity.