The methods for completely measuring the timing jitter of passively mode locked Ti∶sapphire laser are proposed. It is demonstrated that for the laser system with smaller timing jitter, frequency domain measurement is the major method, whereas for the system with larger timing jitter, frequency domain measurement is not suitable. Instead of that the method of using synchroscan streak camera is more precise. With the technique of actively cavity length controlling, the timing jitter of passively mode locked Ti∶sapphire laser has been reduced from 6.6 ps (before controlling) to 0.47 ps.