The Space multi-band Variable Objects Monitor (SVOM) is an astronomical satellite jointly developed by China and France, primarily focused on the detection of gamma-ray bursts (GRBs) and transient sources. The SVOM satellite was launched on 2024 June 22, with four payloads installed onboard. As one of payload, Gamma-Ray Monitor (GRM) comprises three gamma-ray detectors (each detector has an effective area of approximately 200 cm2) with distinct pointing directions, enabling the temporal and spectral measurements as well as localization of GRBs in the energy range of 15–5000 keV. This article first introduces the on-board localization algorithm design for GRM and presents preliminary test results. Then, leveraging abundant ground-based computational resources, a joint fitting method for spectral and localization analysis using Monte Carlo Markov Chain (MCMC) is implemented. In contrast to the on-board localization algorithm, the on-ground MCMC method comprehensively considers the influence of spectral characteristics, thereby mitigating systematic biases. Finally, a systematic analysis based on this method is provided, highlighting the localization and spectral measurement capabilities of GRM. The preliminary localization analysis result for the on-board detected GRB 240629A by both GRM and Fermi/GBM shows that the localization result (error ∼ 4°.14) of GRM is consistent with the Fermi/GBM result.

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