This study is a single-arm, open-label, single-dose, dose-escalation, and dose-expansion trial, aiming to assess the safety and tolerability of YOLT-203 in Chinese patients with Primary Hyperoxaluria Type 1 (PH1), and to preliminarily evaluate the effect of a single dose of YOLT-203 on plasma oxalate levels. In this study, the maximum duration of the screening period is 60 days, with the treatment day being Day 1 (D1), and the safety follow-up period extending to the 52nd week after dosing. Additionally, in the dose-escalation phase, after the first dose cohort, investigators will conduct a comprehensive evaluation based on safety, pharmacokinetic (PK), and pharmacodynamic (PD) data, and following discussion at the Safety Review Committee (SRC) meeting, subjects may voluntarily receive a second administration of the study drug at an effective dose level. After the completion of the main study, subjects will undergo long-term follow-up. In accordance with the requirements of the "Technical Guidance for Clinical Research on Long-term Follow-up of Gene Therapy Products (Trial)" issued by the Center for Drug Evaluation (CDE), long-term follow-up will be conducted for up to 15 years after dosing.