Lobster-eye is an optical focusing system that simulates the lobster vision, and is very suitable for appling in the X-ray pulsar imaging detection on the satellite platforms. Based on the principle of grazing incidence, theoretically quantitive relationship between photon energy and full reflection critical angle and reflectivity for different metallic film are studied. A method for calculating the effective detection area of the Angel lobster-eye optical system is proposed, and formulas are duduced. Montel-Carlo experiment results is agree with the theoretical figure. In the range of 1~10 keV, the effective detection area of the lobster-eye optical system is approximately negative exponential function of photon energy, specific parameters depending on film roughness.