The transient transmission error of capacitor voltage transformer（CVT） may cause malfunction of protection relays. To solve this problem， an integral equivalent transformation based method for CVT transient error corrections is proposed. Using trapezoidal integral equivalent transformation， the high-order equivalent circuit of CVT can be transformed into a simple DC circuit just containing DC current sources， resistors and a DC voltage source. Then the nodal voltage equations of the circuit can be established. By solving these simple linear equations， CVT's primary side voltage can be calculated accurately using its secondary side voltage collected. The decomposition of normal component and fault component is used to solve the initial value problem of the algorithm. A digital low-pass filter is used to remove the high-frequency interference signals. Simulation results testified the accuracy and effectiveness of the correcting method.