This study is a multicenter, randomized, double-blind (with open-label dose levels and active comparator), parallel-group, placebo- and active-controlled Phase 2 clinical trial aimed at evaluating the efficacy, safety, immunogenicity, and pharmacokinetic (PK) characteristics of HDM1005 in subjects with Type 2 Diabetes Mellitus (T2DM) who have inadequate glycemic control after diet/exercise or metformin therapy. A total of 216 subjects will be enrolled. All subjects will be stratified by baseline HbA1c levels (≤8.5% or \>8.5%) and prior metformin use, then randomized 1:1:1:1:1:1 to: Group 1 (HDM1005 0.5 mg), Group 2 (HDM1005 1.0 mg), Group 3 (HDM1005 2.0 mg), Group 4 (HDM1005 3.0 mg), Group 5 (Placebo), and Group 6 (open-lable dulaglutide 1.5 mg, active comparator), with 36 subjects in each treatment group. Within each dose cohort (0.5/1.0/2.0/3.0mg), there will be \ 45 total subjects (36 HDM1005 + 9 placebo). The 1.0mg, 2.0mg, and 3.0mg cohorts will implement dose titration. The study consists of: 2-week screening, 20-week treatment, and 4-week safety follow-up. The end-of-study visit will be conducted 28 days after the last administration cycle.