Objective To compare the effects of three different lengths of peripheral venous catheters for blood collection in surgical patients with obesity combined with metabolic syndrome. Methods The inpatients of a tertiary general hospital in Zhejiang Province from April 2023 to June 2023 were selected as the study subjects using the fixed-point consecutive sampling method. The patients were divided into three groups by simple randomized controlled method,with blood collection via a mini-midline catheter in experimental group 1,via midline catheter in experimental group 2,and peripheral venous indwelling needle in the control group. The overall success rate of blood collection,survival analysis of first blood collection failure,success rate of first blood collection,specimen qualification rate,and incidence of catheter-related complications were compared among the three groups. Results A total of 162 patients were included,with 54 patients in each group. The total success rates of blood collection in experimental group 1,experimental group 2 and control group were 53.70%,88.89%,and 31.48%,respectively. The results of two-by-two comparisons showed that the differences were statistically significant(P<0.017) when comparing experimental group 1 and experimental group 2,experimental group 2 and control group. The differences were not statistically significant(P>0.017) when comparing experimental group 1 and the control group. The total rates of catheter-related complications in experimental group 1,experimental group 2 and control group were 33.33%,14.81%,and 40.74%,respectively,and the difference was statistically significant(P<0.05). A two-by-two comparison of the results showed that the difference between the experimental group 2 and control group was statistically significant(P<0.017) and there was no statistically significant difference comparing the experimental group 1 and experimental group 2,and experimental group 1 and control group(P>0.017). Regarding the time of he first blood collection failure,it was 4.00(3.36,4.64) and 3.00(2.25,3.75) d for experimental group 1 and control group,respectively,and the difference was statistically significant when comparing the three groups(Log Rank,P<0.001). Conclusion The three peripheral venous catheters can be used for the first blood collection in patients with obesity combined with metabolic syndrome. When collecting blood via a midline catheter,the time of first blood collection failure is later,the overall success rate of blood collection is higher,and overall incidence of catheter-related complications is lower.