Due to low pressure，complex circumstance noise and weak leakage signal of the urban underground gas pipelinre，it was difficult to detect the signal by general signal processing method which is based on the second-order cumulants．According to higher-order cumulants and bispectrum theory，bispectrum was applied to non-Gaussian signal detection in Gaussian noise，the frequency resolution was improved in bispectrum through the direct method of bispectrum estimates and the use of two-dimensional window，setting up the corresponding hypothesis testing model in actual situation．Experimental results show that the method can be validated to detect leakage signal of low-pressure gas network，the detection distance is not less than 20m．