After the satellite is separated from the upper stage, the initial attitude is not learned about since the attitude sensors are not valid for the measurement. In order to solve this problem, an initial attitude calculation method using multi sensors’ intercalibration was designed. The kinematic equation was set firstly, and then the first available attitudes measured by star sensor as well as gyro’s angular velocity were prepared. The nonlinear equation was solved by using the trust region algorithm; meanwhile the attitude was obtained from backward to forward; the analog sun vector detector’s information was used to revise the deduction; a convenient method translating the attitude from the sun to the earth was put forward; sun vector was connected to star sensor’s information. The deduction result is consistent with injection attitude of rocket. Simulation result on the ground was compared with the real attitude in orbit, validating the correctness of simulation model. The result provides support for the design of satellite and the procedure design and improvement of flight.