Two novel metal-organic frameworks (MOFs), HBNU-1 and HBNU-2, have been synthesized successfully. We adopt a step-by-step assembly strategy, which first synthesize the Cu-3 cluster Cu-3(mu(3)-OH)-(pz)(3)(CH3COO)(2)(Hpz), and then react it with H2BDC under different conditions to form final frameworks. In both MOF structures, the Cu-3 clusters are maintained, although certain differences are observed. Compared with HBNU-1, the Cu-3 cluster dimerizes into Cu-6 cluster in HBNU-2. With this step-by-step cluster assembly strategy, MOF structure predicting becomes possible and may give some reference for MOF structure designing.