In this work, we achieved a self-takeoff of an eagle-scale flapping-wing robot for the first time. Inspired by the takeoff process of Ospreys, we propose a bio-inspired takeoff strategy, then discuss the dynamic model and the requirements for self-takeoff. Based on the requirements of flight strategy, we designed a system with two parts, including a flapping-wing aircraft with a wingspan of 1.8m and a take-off weight of 870g, and an auxiliary platform with an initial pitch angle adjustment function. In order to explore the differences in the take-off process under different conditions, we conduct the flight experiments under different time-averaged thrust-to-weight ratios (0.745-0.876) and launch angles (45°-90°). The results of flight experiments confirmed the theoretical analysis that the flapping-wing robot can achieve self-takeoff with no potential energy cost and maintain high maneuverability (The video shows a rapid climb immediately after takeoff) even when the time-averaged thrust-to-weight ratio is smaller than 1. This is significantly different from conventional rotary-wing and vertical take-off and landing (VTOL) UAVs. This work solves the challenge of self-takeoff for large-scale flapping-wing robots using a designable method and demonstrates the superior performance potential of flapping-wing robots compared to conventional UAVs.