Low-maturity shale oil in-situ development refers to artificially heating underground low-maturity shale oil reservoirs, cracking the internal cheese root into oil and gas and then delivering it to the surface through a corresponding process, which needs to control the horizontal well network spacing in the range of 4–10 m, and the error rate of the borehole trajectory control is < 5%, and the domestic magnetic guided drilling technology is well applied in thick oil, but the error is still larger in the process of constructing the network of small spacing wells. However, the error is still large in the construction process of a small well spacing well network. Based on the existing rangefinder ranging mechanism, the article analyzes that the use of the layout to enhance the triaxial magnetic signal density can effectively improve the signal sharpness, so as to solve the high-precision guidance problems in the in-situ development of low-maturity shale oil. To this end, on the basis of the previous design, we optimized the arrangement of magnetic beacons, calculated the signal strength by using finite element software and compared it with the original design, and found that the signal sharpness had been improved obviously; we built a simulation test device for magnetic ranging in shale oil in-situ development with small well spacing and carried out the ground physical test of ranging error in double horizontal wells, and the test results showed that the signal error value before and after the optimization had been reduced obviously, which better meets the problem of accurate guidance. The test results show that the signal error value before and after the optimization has been significantly reduced, which better meets the drilling requirements of precise guidance; the field test was carried out at a well location in the Xinjiang oilfield, and the test results show that the rangefinder meets the design and application indexes. This optimization method provides technical ideas for the in-situ development of low-maturity shale oil, which is of guiding significance.