Objective. To investigate the characteristics of intestinal flora in patients with gastric cancer complicated by coronary heart disease and heart failure and the guiding value of probiotics intervention for clinical treatment. Methods. (1) One hundred and sixty-eight gastric cancer patients with complications of coronary heart disease and heart failure from August 2017 to December 2020 were selected as the observation group. A total of 125 patients with coronary heart disease treated at the same time were selected as control group 1, and 89 healthy subjects were selected as control group 2. Fecal samples were retained to extract the total RNA, and high-throughput sequencing was applied to complete the analysis of microbial diversity and structure differences, so as to obtain the biological species information of the specimens. (2) Patients in the observation group were randomly divided into two equal groups of 84 patients, namely, group A and group B. Group A was treated with conventional methods, and group B was combined with probiotics intervention on the basis of group A; then, the differences in the intestinal mucosal barrier between the two groups were compared. Results. The Chao, ACE, and Simpson index in the observation group were lower than those in control group 1 (
P
<
0.05
), and the Shannon index was higher than that in control group 1 (
P
<
0.05
). The Chao, ACE, and Shannon index in control group 1 were lower than those in control group 2 (
P
<
0.05
), whereas the Simpson index was higher than in control group 2 (
P
<
0.05
). The abundance of Bacteroidetes in the observation group was lower than that in control group 1 and control group 2 (
P
<
0.05
). The abundance of Firmicutes was higher than that of control group 1 and control group 2 (
P
<
0.05
). Four weeks after treatment, the levels of ET, D-lactic acid, and PCT in the group B were (0.10 ± 0.01), (3.99 ± 0.32), and (0.41 ± 0.10), respectively, which were lower than those in group A (0.19 ± 0.03), (4.51 ± 0.46), and (0.81 0.13). Conclusion. Gastric cancer patients with complications of coronary heart disease and heart failure are associated with intestinal flora disorder, which may be involved in the occurrence and development of the disease. Probiotics intervention is helpful to repair the intestinal mucosal barrier in patients, which is worthy of popularization and application.