<h2>The problem</h2>

<p>When I print with my mElephant 3D printer from Makeblock, the prints come out with waved walls like in the picture below. I am using PLA filament from <a href="https://makeblock.lt" rel="noreferrer">https://makeblock.lt</a></p>

<p><img src="https://makeblock.lt/up/so/3d-waves.jpg" alt="3d-waves"></p>

<h2>What I tried</h2>

<p>I tried changing temperatures 190-220, tried to change the flow rate. Also checked if the bolts are not lose. Everything seems good.</p>

<h2>My printer</h2>

<p><img src="https://makeblock.lt/up/so/melephant.jpg" alt="mElephant"></p>

Repeating patterns like that usually stem from issues in the Z axis.  This is likely caused by bent screws which in turn cause the X axis to move around.    Are the top of the threaded rods constrained?  If they are, an easy fix may just be to let the top of the threaded rods float around by removing the constraint.  Most Prusa i3's use 5mm threaded rod for the screws and 8mm smooth rod, does your printer use the same setup?
If your printer has 8mm (or 5/16") threaded rod you could try to get some that are straight or the better solution would be to get the 5mm threaded rods and just print adapters to hold the 5mm nut inside the trap.  This would require new couplers (aluminum or rubber/plastic hose), 5mm threaded rods, nuts, adapters (printed) and a small change to the firmware.  This works because the 5mm rod is more flexible than the 8mm smooth rod and less likely to force the carriage around.
If you already have the 5mm threaded rod/8mm smooth rod then I would look to make sure your X axis is tight and does not move around on the Z axis smooth rods.
This would be easier to point out if you include a picture of your printer.
Edit:
If your printer is the mElephant from Makeblock then I would try removing the bearings at the top that constrain the threaded rods and try the print again.