Abstract: Habitat quality is an important index to measure the habitat function of Yancheng coastal wetland. Under the dual influence of human activities and the expansion of Spartina alterniflora, the habitat quality is threatened. This study took the core area of Yancheng National Nature Reserve as an example, using the InVEST model combined with linear regression equation and the Redundancy Analysis (RDA) to analyze the impacts of human activities and the expansion of Spartina alterniflora on the habitat quality. The results showed that: (1) The human activity intensity index (HAILS) showed a trend of first rising and then declining, with the highest value of 0107 3 in 2006 and the lowest value of 0007 8 in 1992. The area of Spartina alterniflora (ASE) continued to expand, and area percentage increased from 1.673% to 24.930%. In general, habitat quality (HQ) showed a downward trend, from 0.863 to 0.875 in 1983-1992, from 0.739 7 in 2014 to 0.774 8 in 2017. (2) HQ had a significant negative correlation with HAILS and ASE, and the correlation coefficients were -0.940 2 and -0.923 7 respectively. ASE had more influence on HQ than HAILS. (3) RDA ranking can reflect the relationship between HQ, HAILS and ASE. HQ in 10 periods were divided into four quadrants by the variables of HAILS and ASE. The results of RDA ranking were divided into three categories: the first category was in 1983 and 1992 (the first quadrant). The impacts of HAILS and ASE on habitat were relatively weak, and the intensity of their effects was similar. The results in 1997, 2000, 2002, 2006 and 2009 were classified as the second category (the third and fourth quadrants). The influence of HAILS on HQ was greater than that of ASE. The results in 2011, 2014 and 2017 were the third category (the second quadrant). ASE has a greater impact on HQ than HAILS. The results of RDA ranking were with obvious stage characteristics. In 10 periods, the correlation between HQ and HAILS was 1983 ≈ 1992 ＜ 1997 ≈ 2017 ＜ 2000 ≈ 2002 ≈ 2014 ＜ 2011 ＜ 2006 ＜ 2009; the correlation between HQ and ASE was 1997 ＜ 1983 ≈ 1992 ＜ 2000 ≈ 2002 ＜ 2006 ＜ 2017 ＜ 2009 ＜ 2011 ＜ 2014. The results can provide reference for the construction and management of world natural heritage site of Yancheng costal wetland.