A new type of cold atom interferometry gravimeter based on Bragg diffraction was presented, which is able to increase the gravity measurement sensitivity and stability of common Raman atom gravimeters significantly. By comparing with Raman transition, the principles and advantages of Bragg diffraction-based atom gravimeters were introduced. The theoretical model for a time-domain Bragg atom gravimeter with atomic incident direction parallel to the wave vector of Bragg lasers was constructed. Some key experimental requirements for an nth-order Bragg diffraction-based atom gravimeter were deduced, including the temperature of atom sources, the diameter, curvature radius, frequency, intensity, and timing sequence of Bragg pulses, etc. The analysis results were verified by the existing experimental data in discussion. The presented theoretical model and conclusions provide a meaningful reference for the understanding and construction of a Bragg diffraction-based cold atom gravimeter.