Inclusion criteria:  Has a histologically confirmed or cytologically confirmed diagnosis of advanced NSCLC; No known epidermal growth factor receptor (EGFR) mutations or anaplastic lymphoma kinase (ALK) reshoots; Has received prior systemic treatment with first- or second-line PD-(L)1 and platinum-containing dual-agent chemotherapy for their advanced NSCLC; Has measurable disease; Has a performance status of 0 or 1 on the Eastern Cooperative Oncology Group (ECOG) Performance Status; Has adequate organ function; Has a life expectancy of at least 3 months; If female of childbearing potential, have a negative serum pregnancy test within 7 days prior to first trial treatment; If female of childbearing potential or a male subject with a partner with childbearing potential, be willing to use a highly effective method of contraception (with a failure rate of less than 1.0% per year) from first study treatment to 24 weeks after completion of the trial treatment.  Exclusion Criteria:  Untreated active central nervous system metastasis or leptomeningeal metastasis; Is currently participating and receiving an investigational drug or has participated in a study of an investigational drug within 4 weeks or within 5 times of half-life (no less than 2 weeks), whichever is shorter prior to the first dose of trial treatment; Major surgery for any reason, except diagnostic biopsy, within 4 weeks of the first administration of trial treatment and/or if the subject has not fully recovered from the surgery within 4 weeks of the first administration of trial treatment; Curative radiation within 3 months of the first dose of trial treatment; Subjects receiving immunosuppressive agents (such as steroids) for any reason should be tapered off these drugs before initiation of trial treatment (with the exception of subjects with adrenal insufficiency, who may continue corticosteroids at physiologic replacement doses, equivalent to < 10 mg prednisone daily, inhaled steroids and topical use of steroids); Vaccination within 28 days of the first administration of trial treatment, except for administration of inactivated vaccines; Has interstitial lung disease, or a history of pneumonitis that required oral or intravenous glucocorticoids to assist with management; History or current active autoimmune disease that might deteriorate when receiving an immunostimulatory agent; Previous malignant disease; History of uncontrolled intercurrent illness; Prior therapy with any antibody/drug targeting T cell coregulatory proteins; Has received treatment with lenvatinib or docetaxel or VEGFR-TKI; Known severe hypersensitivity reactions to antibody drug; Is pregnant or breastfeeding; Other medical conditions that at the discretion of investigator interfere with the requirements of the trial in terms of safety or efficacy evaluation, or treatment compliance.