As a key component of electron multiplier device, a microchannel plate (MCP) can be applied in many scientific fields. Pure aluminum oxide (Al2O3) as secondary electron emission (SEE) layer were deposited in the pores of MCP via atomic layer deposition (ALD) to overcome problems such as high dark current and low lifetime which often occur on traditional MCP. In this paper, we systematically investigate the morphology, element distribution, and structure of samples by scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS), respectively. Output current of different thickness of Al2O3 was studied and an optimal thickness was found. Experimental tests show that the average gain of ALD-MCP was nearly five times better than that of traditional MCP, and the ALD-MCP showed better sensitivity and longer lifetime.