Patients after abdominal surgery will receive enteral nutrition for 2 days, if she/he can tolerate 30% of goal-dose EN, then she/he will be randomized to Gradual or immediate Goal-dose EN group at day 3. Patients in Gradual Goal-dose EN group will receive increased calories gradually by EN and will reach the 80% of target energy by EN at day 8 while patients in immediate Goal-dose EN group will receive 100% of target energy by EN at day 3 after abdominal surgery. Both groups will receive EN for 5 days except 80% of target energy delivered by oral feeding or patients are discharged from hospital, whichever arrives first. The primary and secondary outcomes will be collected.