How to calculate period of signal with matlab

use autocorrelation. If your data is periodic you should get high correlation once the lag time matches the period. here is an example:

x=0:0.1:20*2*pi;
y=sin(x); % so we know the period is 2*pi roughly 6.28
ac=xcorr(y,y);
[~,locs]=findpeaks(ac);
mean(diff(locs)*0.1)

ans =

      6.2842

x=0:0.01:20*2*pi;
y=abs(cos(10*pi*x));
ac=xcorr(y,y);
[~,locs]=findpeaks(ac);
mean(diff(locs)*0.01)

ans =

      0.1000

Another approach is using FFT, particularly if you have a more complex signal.