This study will take place at multiple sites and is divided into three phases:an initial 4-week getting-to-know-you phase,a 26-week main phase where participants receive medication,and a 4-week follow-up phase.Participants will be divided into three groups:two will receive different doses of PEG-rhGH Injection,and the third will receive hGH Injection.The goal is to determine which medication works best.

Inclusion Criteria:

• Born full-term and "small-for-dates" - Born at 37-41 weeks (full-term). - Birth weight below the 10th percentile for that week of pregnancy and sex .
• At least 3 years old on the day the parent signs the consent form.
• Still prepubertal (Tanner stage I - no signs of puberty yet).
• Height at the first study visit is more than 2 standard deviations below the average for his or her age and sex.
• Bone age on X-ray is no more than 1 year ahead of real age.
• Never taken growth hormone, IGF-1, or any ghrelin-like medicine before.
• Both the subject and their guardian are able to voluntarily sign the Informed Consent Form (ICF) and voluntarily cooperate in completing the trial according to the protocol. If the subject is legally incompetent, written informed consent from their guardian shall be obtained. Additionally, relevant information about the clinical trial shall be communicated to the subject within their understanding, and the subject should be encouraged to sign the ICF personally as much as possible.

Exclusion Criteria:

• Severe allergy to growth hormone or its ingredients.
• Growth-hormone deficiency.
• Any chromosome/genetic/syndrome cause of short stature.
• Other diseases that can impair growth.
• Cognitive, developmental, or psychiatric disorders that could affect assessments .
• Current or past cancer, or high familial cancer risk.
• Positive hepatitis B, hepatitis C, HIV, or active tuberculosis at screening.
• Abnormal liver or kidney blood tests.
• Pre-diabetes or diabetes at screening .
• Systemic steroids > 28 consecutive days or > 14 days total in the last 3 months.
• High-dose inhaled steroids > 28 days in the last year.
• Prior use of aromatase inhibitors, GnRH analogues, sex hormones, anabolic agents, or other drugs that affect growth. 13. Unable to receive subcutaneous injections.
• Claustrophobia or inability to undergo brain MRI.
• Participated in another clinical trial with investigational treatment within 3 months.
• Any other condition that, in the investigator's opinion, makes the child unsuitable for the study.