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Summary: The utility tunnel plays a vital role in improving city comprehensive bearing capacity, while whether the gas pipeline is set into the utility tunnel is a focus as chain and coupling accidents will happen in case of fire and explosion. In this study, a scaled‐down gas chamber experiment was carried out, and full‐scale two‐dimensional (2d) and three‐dimensional (3d) numerical models were compared. The combustion process of premixed gases could be roughly divided into four development stages, that is, (I) rapid development stage, (II) stable development stage, (III) jump stage, and (IV) oscillation stage. The over‐pressure on different walls had the same development trend and the peak value appeared in the jump stage. When the methane‐air premixed concentration was 9% and the ignition source was located at the center of utility tunnel (x = 0 m), the most unfavorable working condition occurred as its peak over‐pressure was about 1.57 MPa with an increase rate of 70%. Similarly, when the ignition position was at the left end (x = −99 m), the peak over‐pressure value was 1.51 MPa, which was 65% more than the initial value. While when the ignition position was not located at the center or ends of utility tunnel, the maximum wall pressure had a "double peaks" characteristic. When x = −80 m, the pressure jumped at 27 and 91 ms with the peak values up to 1.33 and 1.49 MPa, respectively. Arising findings provide guidance for assessing risks of setting the gas pipeline into utility tunnel and help to improve the safety design concept of utility tunnel. [ABSTRACT FROM AUTHOR]