Abstract: Offshore wind power construction is difficult and with high risk. It is extremely difficult to control the cost,of which the construction period is the biggest variable. Firstly,as to adapt to the requirements of cost reduction and efficiency increase in the coming era of flat rate,focused on the offshore seas from the southern Shandong Peninsula to Guangxi,this paper compares the quality of ERA5,CCMPv2 and NCEP reanalysis wind fields based on measured data. Secondly,this paper modifies a SWAN wave model adaptively to perform a numerical simulation with a time span of 25 years（1996-2020）. Utilizing the results of 1-hour hindcast wind and wave data,the weather window and construction efficiency for the pile foundation and upper set of offshore wind turbine are evaluated both on spatial and temporal scope. With respects to the key locations for China offshore wind power development,some construction suggestions are also made. The results indicate that wind data from ERA5 is in best agreement with observations. The accuracy of simulated wave parameters has been improved after the calibration of SWAN model. Besides,workloads of foundation construction and wind turbine installation have significant temporal and spatial variation characteristics in the studied area.