Whether the space-time is curved or not? The experimental criterions to judge this point are: (1) The results of three classical relativistic experiments in essence are favorable to the special relativistic gravitational theory (base in the flat space-time). However they are unfavorable to the general relativity. (2) In the Gravity Probe-B experiment: the gyroscope precession rate of the orbital effect deduced from the special relativistic gravitational theory =(2/3)* the precession rate of geodetic effect deduced from the general relativity, the precession rate of the earth rotation effect deduced from the special relativistic gravitational theory =(3/2)* the square of cos(phi)* the precession rate of the frame-dragging effect deduced from the general relativity, where (phi) is the angle between the projection of gyroscope angular velocity in the equatorial plane and the normal line of orbital plane. If the experimental values are identical with the predictive values deduced from the special relativistic gravitational theory, then the space-time is flat.