I found this solution,here mContext is the context of your activity,i am using it outside the activity.
if (android.os.Build.VERSION.SDK_INT <= android.os.Build.VERSION_CODES.FROYO) {
// only for gingerbread and newer versions
((Activity) mContext).getWindow().addFlags(WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED);
((Activity) mContext).getWindow().addFlags(WindowManager.LayoutParams.FLAG_TURN_SCREEN_ON);
((Activity) mContext).getWindow().addFlags(WindowManager.LayoutParams.FLAG_DISMISS_KEYGUARD);
KeyguardManager manager (KeyguardManager) mContext.getSystemService(Context.KEYGUARD_SERVICE);
KeyguardLock lock = manager.newKeyguardLock("abc");
lock.disableKeyguard();
} else {
KeyguardManager km = (KeyguardManager) mContext.getSystemService(Context.KEYGUARD_SERVICE);
KeyguardLock keyguardLock = km.newKeyguardLock("TAG");
((Activity) mContext).getWindow().addFlags(WindowManager.LayoutParams.FLAG_TURN_SCREEN_ON);
((Activity) mContext).getWindow().addFlags(WindowManager.LayoutParams.FLAG_DISMISS_KEYGUARD);
keyguardLock.disableKeyguard();
PowerManager pm = (PowerManager) mContext.getSystemService(Context.POWER_SERVICE);
WakeLock wakeLock = pm.newWakeLock(PowerManager.FULL_WAKE_LOCK
| PowerManager.ACQUIRE_CAUSES_WAKEUP
| PowerManager.ON_AFTER_RELEASE
| PowerManager.SCREEN_BRIGHT _WAKE_LOCK, "MyWakeLock");
wakeLock.acquire();
}