The present invention discloses a method, apparatus and system for obtaining the tuning capacitance of a Gm-C filter. The method includes: integrating a simulated capacitor within a given time via a current, where the simulated capacitor simulates the capacitor of the Gm-C filter which is set to an even capacitor array; and comparing the integral voltage obtained by the integration with the reference voltage, finding a simulated capacitance that makes the integral voltage equal to the reference voltage via gradual approaching by adjusting a control code, and determining the simulated capacitance as the tuning capacitance. The present invention improves the performance of a Gm-C filter without affecting the performance of the Gm-C filter.