Due to the influence of porosity, conventional fluid factors are difficult to effectively distinguish fluids within complex oil and gas reservoirs, making accurate identification of different fluid types in reservoirs difficult. By constructing an equivalent rock physical model suitable for target reservoirs, fluid and porosity replacement are carried out on this basis, laying the foundation for the construction of fluid factors. To reduce the impact of porosity on fluid identification, a sensitive fluid factor construction method based on adaptive coordinate rotation is proposed, and a practical Gassmann fluid term construction method is proposed through theoretical dissection of fluid factors based on Biot-Gassmann theory. The application effect of actual data shows that the adaptive coordinate rotation fluid factor can reduce the influence of porosity on fluid identification, while the Gassmann fluid term can significantly reduce the misleading effect of porosity on fluid identification, its sensitivity of fluid identification is much higher than that of commonly used fluid factors, which is helpful for high-precision fluid identification of complex oil and gas reservoirs.