Based on data synthesis simulation and air-gun source signal processing，weak signal extraction performances under strong background noise of three different stack methods of linear，phase weighted and S transform are evaluated systemically and reliability of stack results are estimated quantitatively with the indexes of signal to noise ratio，waveform correlation coefficient and phase shift. After a comprehensive discussion and comparative analysis of stack results with above three methods，we conclude that linear stack has the minimum waveform distortion though its signal-to-noise ratio is lower；phase weighted stack has highest signal-to-noise ratio and small phase shift，but its waveform quality has larger deviation compared with linear stack results；S transform stack obtains a relatively higher signal-to-noise ratio and small waveform amplitude loss，but with the certain existence of the phase shift phenomenon. Therefore，linear stack technique is proposed when waveform amplitude and time precision requirements are higher，but the selection of stack methods should be biased when air-gun source firings are limited；S transform stack method should be chosen when there is requirement of high waveform fidelity；and phase weighted stack method should be chosen when there is high time precision in order to achieve effective extraction of weak signal reasonably.