Patients after abdominal surgery will attempt enteral nutrition support for 2 days, if she/he can not tolerate 30% of target energy, then she/he will be randomized to early PN group or late PN group at day 3. Patients in early PN group will receive supplemental parenteral nutrition at day 3 while patients in late PN group will not receive supplemental parenteral nutrition until day 8 after abdominal surgery. Both groups will receive SPN except 80% of target energy delivered by EN or oral or patients are discharged from hospital. The primary and secondary outcomes will be collected.