The angular response function F(θ, φ) is used as an airborne gamma spectrometer to measure the basic physical quantity of the contribution of each nuclide to the total dose rate by the all-energy peak method, which is facing the difficulty of experimental calibration. In this paper, the Monte Carlo program MCNP5 is used to calculate the full-energy peak angle response function F(θ, φ) of a single NaI(Tl) crystal (40 cm × 10 cm × 5 cm) to Cs-137. It has been verified that when the point source is directly below the spectrometer, the relative error between the dose rate calculated by a single crystal γ spectrometer using the all-energy peak method and the dose rate measured by the high-pressure ionization chamber does not exceed 15%. When the distance between the crystal and the point source is 7 m and the elevation and azimuth angles are both 45°, the relative error between the two is 13.891%, which verifies the feasibility of the analog scale of the angular response function.