I found info here - https://learn.sparkfun.com/tutorials/ad … -guide/all, it introduce a level converter between all ADXL345 pins and Arduino UNO pins, but I found on my ADXL345 module, there was only connection between VDD of 5v, the other pins were all break-out there. Could I connected it to Arduino UNO pins directly?
The ADXL345 is a 3.3V device. If you connect it to 5V it will be destroyed.
You can connect it directly to a 3.3V Arduino.
It’s also important to remember that even if you connect VCC on the ADXL345 to 3.3 volts, an Uno’s I/O lines run at 5 volts. 5 volts appearing on the ADXL345’s I/O lines will also kill it.
You must use a level shifter when connecting to a 5 volt board even if you connect power to 3.3 volts. If you don’t want to use a level shifter jremington’s advice is good, you could use a 3.3 volt Arduino like a Pro Mini, or a [RedBoard Plus with the switch on the board set to 3.3 volts.](https://www.sparkfun.com/products/18158)