A pitch angle adjusting device of a picture frame comprises a platform, a stepping motor, a hinge, a worm, a worm supporting arm, a worm gear, a worm gear supporting frame, a lead screw, a lead screw supporting arm, a motion assembly, the picture frame, a picture frame supporting seat, an angular instrument and a computer. The problems that due to limiting instability of a spring mechanism, the angle of an optical element drifts, and due to the fact that dead areas exist in the reciprocating motion of a guide rail mechanism, repeated locating precision is reduced are solved. The motion assembly comprises two inner rings, two outer rings and outer ring fixed sleeves. The pitch angle adjusting device has the advantages that rigid connection and structural stability between structural parts are good, the pitch angle precision of the picture frame is adjustable, the device is light and easy to maintain, the pitch angle adjusting device is applied to an optical element of a high-power laser device to adjust the angle, and batch production can be achieved.