Stability is one of most important performances of an atomic clock.Here we describe our recent work on improving the stability of our 40 Ca+ optical clock.State preparation is adopted to transfer the ion to the groundstate magnetic sublevel of the clock transition,after the quenching laser transfers the ion to the ground state at each cycle.Using this method,the stability for 40Ca+ optical clock is improved to about 6.3 × 10-15/√τ.Compared with 1.0 × 10-14/√τ in previous work,the averaging time is decreased to reach a given level of statistical uncertainty in a clock comparison.