Abstract: Charged particle-induced radioactive capture reaction is a major topic in nuclear astrophysics, significant to understand stellar nucleosynthesis．At astrophysical temperature (Gamow window), the cross area of these reactions is small, γ ray yields are extremely low, therefore high-efficiency summing γ detection array is needed in cross section measurements．Bayesian analysis was used here to develop an analytical method for γ spectrum of 4π detection array．The method was applied to analyze data of 259 keV resonance of ¹⁴N(p, γ)¹⁵O and 304 keV resonance of ²⁵Mg(p, γ)²⁶Al measured at Jinping Underground Nuclear Astrophysics experimental facility．The new method was found to reduce significantly uncertainty in γ summing peak efficiency．