By considering that the present spacecraft attitude control thruster faul t diagnosis systems have limited functions and have not involved low leakage fau lt diagnosis， a scheme for spacecraft attitude control thruster fault diagnosis i s proposed based on nonlinear attitude dynamics and improved Maksimov nonlinear input estimate algorithm. According to the estimated spacecraft attitude control input from Maksimov algorithm, thrust effectiveness factor is calculated and th e detection of thrust loss is carried out, and based on absolute optical encoder , reaction torque estimate of flywheel is presented and the detection of propell ant leak, especially low propellant leak is implemented. Thrust loss and propell ant leak faults are simulated and diagnosed by the proposed scheme, and the effe ctiveness and practicality of the scheme are demonstrated.