The invention discloses a vernier caliper of the pitch interval of bars with internal spline, which comprises spherical measuring heads, a secondary ruler and a main ruler. The main ruler is a right-angled component, scales are arranged on a transverse rod of the main ruler, and a lower vertical rod of the main ruler is a left measuring jaw. The secondary ruler is a right-angled component, a lower vertical rod of the secondary ruler is a right measuring jaw, scales are arranged on the surface of a transverse rod of the secondary ruler, and the secondary ruler body is sheathed on the transverse rod of the main ruler and can move in left and right direction. The spherical measuring head is respectively assembled on the outer lateral surfaces of the left measuring jaw and the right measuring jaw, and two spherical measuring heads are positioned at the same shaft line and parallel to the transverse rod of the main ruler. When in actual measurement, the spherical measuring head is correspondingly selected according to the size of the internal spline measured, zero-calibration is implemented according to the size of the pitch interval of design bars of the internal spline measured, and the size that deviates from a zero position in actual measurement is a deviation value. The vernier caliper of the pitch interval of bars with the internal spline has convenient measurement, accuracy, high efficiency and no special environmental requirements in measurement, and is particularly suitable for being used as a measuring tool for detecting the pitch interval of the bars with internal spline in batch in a production spot.