Abstract: A static test and theoretical analysis were conducted to investigate the service performance of concrete T-shaped beams strengthened with externally CFRP tendons under short-term loading, and the calculation method of short-term deflection was explored. The test results indicate that the load-midspan deflection curves of strengthened beams can be simplified as a tri-segmentsegment line. The average strains of concrete and CFRP tendon of strengthened beams basically vary linearly over the depth of the beams at the midspan section before cracking. The average strain of CFRP tendon is obviously less than the strain of bottom concrete after cracking. Based on the test results, the reduction coefficient of cracking stiffness and the bonding characteristic coefficient of CFRP tendons were calculated, and the calculation formula for the short-term deflection on beams strengthened with externally prestressed CFRP tendons was proposed in term of an effective inertia moment method considering the influence of second order effects, and it can provide a reference for practical engineering design.