Abstract: The logging while drilling tool with controllable neutron source has been available commercially abroad. To shorten the gap from abroad, the neutron LWD tool with controllable neutron for porosity logging is developed, and it has been successfully introduced and applied in some oilfields domestically. Based on the proceedings of the technique at home and abroad, the research logic of the self developed tool is illustrated. The controllable sources are used to emit neutrons towards the formation and to acquire the relative formation information. The design works on detector structure, detector position, neutron generator and neutron tube are instructed and optimized through the combination of theoretical modeling, experimental verification and practical applications. The acquisition of porosity and macroscopic capture cross section are carried out through integrating them into one collar. The two parameters can be measured in one logging trip, and gas-bearing layer and water saturation can be identified. Therefore, the technique can save time and cost of logging.