This study evaluates the maintenance strategy based on risk stratification and MRD status after stem cell transplantation.

This is a single-arm, multicenter, prospective study. Participants who are R2-ISS 1,2 and MRD negative receive the single drug lenalidomide maintenance. In other circumstances, for example, patients who are R2-ISS 3 or 4 will receive daratumumab combined with lenalidomide regardless of MRD status, while patients with MRD positivity will also receive daratumumab plus lenalidomide maintenance.

Inclusion Criteria:

1. Newly diagnosed multiple myeloma with a history of a minimum of 4 cycles of induction therapy, have received high-dose therapy (HDT) and autologous stem cell transplantation (ASCT) within 12 months of the start of induction therapy, and be within 6 months of ASCT.
2. Must have a partial response (PR) or better response before maintenance.
3. Must have an Eastern Cooperative Oncology Group performance status score of 0, 1, or 2.
4. This study allows for post-ASCT consolidation therapy.
5. ANC ≥ 1.0 x 10^9/L, Hb ≥ 85 g/L PLT ≥ 75 x 10^9/L (if BMPC < 50%) or PLT ≥ 50 x 10^9/L (if BMPC ≥ 50%).
6. No active infection.
7. a).TBIL<1.5 x upper limit of normal (ULN) (<3 x ULN in patients with Gilbert's syndrome); b).AST and ALT <3 x ULN.; c. Creatinine clearance ≥ 45mL/min.

Exclusion Criteria:

1. Must not refractory or non-tolerate to lenalidomide in Arm A.
2. Must not refractory or non-tolerate to lenalidomide and daratumumab in Arm B.
3. Must not have progressed on multiple myeloma (MM) therapy before screening
4. Chronic obstructive pulmonary disease (COPD) with FEV1 less than 50 % of predicted normal；
5. Have known moderate or severe persistent asthma within the past 2 years or current uncontrolled asthma of any classification
6. History of stroke or serious thrombotic event within 12 months prior to screening.