To develop an investigation form for postoperative infection outbreak (PIO), and to identify sources of the outbreak in the early stage. After an exhaustive literature review, we used the Delphi method to determine the indicators and relative risk scores of the assessment tools through 2 rounds of specialist consultation and overall consideration of the opinions and suggestions of 20 specialists. A total of 203 studies of PIO were eligible for inclusion. The mean authority coefficient (Cr) was 0.87. Kendall’s W coefficient of the specialist consultation was 0.704 after 2 rounds of consultation (P < .005), suggesting that the specialists had similar opinions. Based on 4 primary items and 19 secondary items of the source of PIO, and tripartite distribution characteristics of infected patients, we constructed the PIO investigation form. The PIO investigation form can be used in the investigation of the early-stage cluster of cases, it’s a prerequisite for taking effective control measures, avoiding PIO occurrence. However, the effect of the investigation form needs to be further evaluated. •Postoperative infection outbreak investigation differs from individual infection.•Identifying the source of the outbreak is the most crucial aspect of investigation.•The investigation form provides a reference for infection preventionists.•The Delphi method combined with literature research is better than traditional.