Agriculture has both economic value and non-economic value. The calculation of the non-economic value of agriculture has become a research hotspot in academic circles. This paper divides the value of agriculture into products production value and ecological value, and adopts an authoritative ecological value calculation idea, i.e. the method proposed by Costanza et al. in 1997 as the basis to calculate the ecological value of agriculture. However, the study has come under heavy criticism: for example, some data have major deviation, underestimating the ecological value of cultivated land while overestimating the wetland. XIE Gaodi et al. in 2003 came up with more reliable results to make up for the deficiency of the methods from Costanza et al. Referring to some of the results and on the basis of a questionnaire survey to 200 Chinese ecologists, this paper presented an equivalent factor table for evaluating the ecological service value (ESV) of China's ecosystem. Based on this table and the practical situation of Tianjin, the paper formulates an applicable calculation method for ecological value and actually calculates the ecological value of agriculture in Tianjin with official statistics. The results show that the actual value of the ecological value of agriculture in Tianjin in 2012 was 111.20 billion CNY, about triple of the economic value of agriculture (37.56 billion CNY) in the same year.