The invention discloses a battery piece aluminum back surface field voidage test method. The method comprises the following steps of: S1, putting the back surface of a sample on a separator upwards; S2, dropping a humectant into the region to be tested at the surface of the sample, and then performing standing; S3, scraping the aluminum paste of the region to be tested by a scraper, wherein the scraper and the surface of the sample form an acute angle when scrapping is performed; S4, washing the surface of the sample by employing a cleaning agent, and drying the surface of the sample; S5, fixing the processed sample to a 3D microscope test board; S6, selecting a low power lens, regulating the displacement of the test board to allow a lens to face the center position of the region to be tested, performing focusing regulation of the lens to make an image in a view window most clear, performing fine tuning of the displacement to generate most laser opening numbers N in the test view window, measuring and recording the length Ln of each laser opening line void region, and calculating the measured voidage according to the formula; and S7, moving the test platform to continuously executethe step S6 for the region to be tested for many times, and obtaining an average value, namely the voidage of the region to be tested.