Abstract: The flood peak flow was recalculated due to the change of underlying surface conditions in the confluence area of Shiji waterway mouth of Pidong trunk canal, and the design flood peak flow was determined by rationality analysis to flood occur once in 20 years and once in 50 years at Shiji waterway mouth of Pidong trunk canal. According to the calculation results and the safety requirement of the channel operation, the policy suggestion that the channel level should be adjusted to grade Ⅱ and the flood control standard should be adjusted to once in 30 years is put forward.