The invention provides a novel HOM interference theory based gravity instrument. The instrument comprises an entangled source (1), a delayer (2), a first beam splitter (3), a stress sensor (4), a prism (5) to be dropped, a reference prism (6), a second beam splitter (7), a first detector (8), a second detector (9), a coincidence measurement logic calculator (10), an atomic block (11) and a controller; when in use, the delayer (2) is adjusted to delay to enable destructive interference between the idle light and signal light flowing through the initial position, then the prism (5) to be dropped freely falls down to the end position, the free falling time is recorded, the delayer (2) is adjusted to delay again to enable destructive interference between the idle light and the signal light flowing through the end position, and finally the gravity acceleration can be obtained through the controller according to the difference between two delay, and the difference between the initial time and the end time. According to the instrument, the HOM interference theory is utilized to achieve the high precision measurement of the gravity accelerator; the instrument can be widely applied to the fields of metering, surveying and mapping, physical geography, ocean exploration and space science.