In this paper, we propose a novel cell self-loading and patterning device for quantitatively study density effect on cell behaviors. Using this device, it is easy to gather different cell density colonies in different sizes of micro-chambers using one homogeneous cell solution. As a demonstration, we show that the cell number of self-patterning MCF-7 colony is in proportion to the size of liquid-absorbing cavity in the device, from single cell to tens of cells. This device can easily be used to compare the cancer cells' proliferation in different micro-environments, such as the same number of cells in micro-cavities with different sizes, or different numbers of cells in micro-cavities with the same size, or with different FBS concentrations. Our studies imply a plausible positive correlation between the local concentration of autocrine factors and tumor cell proliferation, which is also quantitative analyzed by a simple model.