Purpose Psoriasis is an immune-mediated chronic inflammatory disease. Metabolic syndrome (MetS) is characterized by central obesity, hypertension, dyslipidemia, diabetes and insulin resistance (IR). Increasing evidence indicates that psoriasis is associated with MetS. This study aimed to explore some metabolite indexes which could evaluate the severity or predict the risk of psoriasis patients associated with MetS. Patients and methods It was a case-control study conducted in Beijing Hospital of Traditional Chinese Medicine. Sixty healthy volunteers (HC), 100 patients with psoriasis (Ps), 100 patients with MetS (MetS) and 80 patients with both psoriasis and MetS (Ps+MetS) were entered between January 2016 and December 2018. Blood samples were taken after at least 12 hours fasting and the contents of trimethylamine N-oxide (TMAO), carnitine, choline and betaine in serum were measured by Liquid Chromatography Mass Spectrometry (LC-MS/MS). Besides, the serum levels of low-density lipoprotein (LDL), high-density lipoprotein (HDL), cholesterol (CHO), triglyceride (TG), blood glucose (BG), creatinine (Cr), urea nitrogen (BUN), uric acid (UA) were determined. Results The non-healthy groups had different degrees of dyslipidemia, Ps-MetS> Ps >MetS. Compared with HC, the Ps had a higher level of TG; The MetS had the lowest level of HDL; The Ps+Mets had the highest level of TG and CHO. The Ps and Ps+MetS both had high level of UA, but there was no difference between the two groups. As for intestinal metabolites, the Ps had significant differences in TMAO, carnitine, and betaine in comparison with HC. The MetS had the highest level of TMAO. There was positive correlation between PASI and TMAO and betaine. Conclusions TMAO and betaine could serve as indexes reflecting the severity of psoriasis. TG, CHO, LDL and UA could serve as risk factors of MetS in psoriatic patients.