A printing head assembly (100, 100a), adapted to drive at least two filaments (F1, F2) to form on a base layer-by-layer to construct a three-dimensional object, the printing head assembly (100, 100a) comprising: a fixing member (110, 110a), having an inlet side and an outlet side opposite to each other; at least two nozzle heads (120a, 120b), respectively disposed at the outlet side of the fixing member (110, 110a), and each of the nozzle heads (120a, 120b) having a filament connection tube (126a, 126b) and a material extrusion port (122a, 122b) respectively penetrating through the fixing member (110, 110a), wherein the filament connection tube (126a, 126b) has a position-limiting portion (128a, 128b); at least two driving units (130a, 130b), respectively disposed at the inlet side of the fixing member (110, 110a), and respectively driving the corresponding filament (F1, F2) to feed into the material extrusion port (122a, 122b) of the corresponding nozzle head (120a, 120b) from the corresponding filament connection tube (126a, 126b) through the fixing member (110, 110a); at least two position-limiting members (140a, 140b), respectively disposed between the corresponding driving unit (130a, 130b) and the fixing member (110, 110a), and connected to the corresponding filament connection tubes (126a, 126b); and at least two position-restoring members (150a, 150b), respectively disposed between the corresponding position-limiting member (140a, 140b) and the fixing member (110, 110a), and located on the corresponding filament connection tube (126a, 126b), wherein each of the filament connection tubes (126a, 126b) respectively leans against the fixing member (110, 110a) through the corresponding position-limiting portion (128a, 128b) or the corresponding position-limiting member (140a, 140b), so as to limit the material extrusion port (122a, 122b) of each of the nozzle heads (120a, 120b) to move between a first height level and a second height level through the corresponding driving unit (130a, 130b) and the corresponding position-restoring member (150a, 150b). a fixing member (110, 110a), having an inlet side and an outlet side opposite to each other; at least two nozzle heads (120a, 120b), respectively disposed at the outlet side of the fixing member (110, 110a), and each of the nozzle heads (120a, 120b) having a filament connection tube (126a, 126b) and a material extrusion port (122a, 122b) respectively penetrating through the fixing member (110, 110a), wherein the filament connection tube (126a, 126b) has a position-limiting portion (128a, 128b); at least two driving units (130a, 130b), respectively disposed at the inlet side of the fixing member (110, 110a), and respectively driving the corresponding filament (F1, F2) to feed into the material extrusion port (122a, 122b) of the corresponding nozzle head (120a, 120b) from the corresponding filament connection tube (126a, 126b) through the fixing member (110, 110a); at least two position-limiting members (140a, 140b), respectively disposed between the corresponding driving unit (130a, 130b) and the fixing member (110, 110a), and connected to the corresponding filament connection tubes (126a, 126b); and at least two position-restoring members (150a, 150b), respectively disposed between the corresponding position-limiting member (140a, 140b) and the fixing member (110, 110a), and located on the corresponding filament connection tube (126a, 126b), wherein each of the filament connection tubes (126a, 126b) respectively leans against the fixing member (110, 110a) through the corresponding position-limiting portion (128a, 128b) or the corresponding position-limiting member (140a, 140b), so as to limit the material extrusion port (122a, 122b) of each of the nozzle heads (120a, 120b) to move between a first height level and a second height level through the corresponding driving unit (130a, 130b) and the corresponding position-restoring member (150a, 150b).