As China is expecting a rapid development in offshore wind power， understanding its output characteristics is of great importance for its accommodation problem. By combining practical data analysis and simulation technology， a comparative study is made on the characteristics of offshore and onshore wind power output. A novel index called distribution characteristic index of wind power output is proposed to measure the features of wind power probability distribution. Stochastic and fluctuation characteristics of inshore wind farms are analyzed using the measured historical data. Offshore wind power outputs are obtained and analyzed using simulation technology with parameters from field measurement and the planning scheme. Results show that offshore wind power has higher output and lower hourly variations compared with onshore wind power， and that offshore wind power has higher output in winter than in summer as the output at night than during the day. Meanwhile offshore wind power has higher distribution characteristic index compared with onshore wind power. Discussions on offshore wind power accommodation are also reported.