Abstract: Abstract: The existing manual excavation and fertilization in orchards are limited by intense labor and low efficiency, and the trench fertilizer machine and the insertion and fertilizer machine inevitably damage the soil surface and the root system of fruit trees due to soil turning. For these reasons, we developed a caterpillar self-propelled gas explosion insertion and fertilizer machine according to the requirement of insertion and deep fertilization in orchards in Xinjiang and other arid regions of north China. This machine solved the key technical problems of fast insertion in hard soil layer, quantitative fertilizer fetching and discharge, and high-pressure gas explosion deep fertilizer application. Based on the rationale of fertilization via high-pressure gas explosion, this machine injected high-pressure air and quantitative fertilizers into root soils simultaneously through the insertion and injection at the fertilization parts of fruit trees, and thereby realized gas explosion subsoiling and quantitative deep diffused fertilization. During the gas explosion loosening in deep soil, the fertilizers were impacted and crushed by high-pressure air flow, and diffused along the loosening fractures into the root soils. This machine adopted the full-hydraulic drive crawler walking mode and was mainly composed of an insertion fertilizer injection device, a quantitative fertilizer application device, an air explosion device, and hydraulic and pneumatic transmission systems. With a compact structure the complete machine met the space requirement for orchard operations at the row space above 2.5 m, and could finish multiple procedures at one time, including fixed-point insertion, gas explosion soil loosening, and quantitative deep fertilization at the root soils of fruit trees owing to the control flexibility and high automation. This protective soil improvement machine integrating "no-tillage, deep loosening and fertilization" could finish deep loosening alone or combine with quantitative fertilization. With the insertion and fertilizer injection device, the insertion (fertilization) depth could be controlled by the knock-in hoisting mechanism. Under the combined action of hydraulic ram suppression and the hammering device, this mechanism could fast insert in the hard tillage layer or the harden layer and shorten the insertion time, improving efficiency. Also a rotating-wheel quantitative fertilization device driven by the hydraulic ram was designed, and the single feeding volume was about 100 ml, but it could be adjusted by increasing the times of fertilization. The gas explosion device offered stable air pressure for gas explosion and deep loosening. Good effects of loosening and fertilization were obtained within the gas explosion pressure of 0.6-0.8 MPa, and the device did not damage roots. To improve the operating efficiency and fertilization effect of this machine, we conducted quadratic rotation orthogonal combination tests by using the single operation time and fertilizer diffusion radius as the evaluation indices as well as the insertion depth, fertilizer rob inner diameter and gas explosion pressure as the influencing factors. Mathematical regression models between the evaluation indices and influencing factors were built on Design-Expert V8.0.6.1, and the effects of significant influence factors on the evaluation indices were analyzed. The optimal combination of influence factors was found to be: insertion depth at 600 mm, fertilizer rob inner diameter of 30 mm and gas explosion pressure at 0.6 MPa. Field verification tests showed the single operation time and fertilizer diffusion radius under the optimal factor combination were 22.1 s and 413.6 mm respectively. We also entrusted Xinjiang Agriculture and Animal Husbandry Machinery Product Quality Supervision and Management Station to test the operational performance of this machine, which indicated this machine could work stably and efficiently, and all tested indices met the technical requirements of prototype design. This study results can provide technical support and reference for the development and modification of the gas explosion subsoiling and fertilizer machine for orchards.